Thinking about Crossfire - should I go for i7?

[Mondozei]

So I bought myself a new PC right during the Black Friday sales last year where I got most of what I needed. I'm using a Sapphire 290 Tri-X as of now and an i5 Haswell.

I'm thinking about picking up a second 290 Tri-X once the Maxwell/Tonga GPUs are out this autumn and the inevitable price drops begin for this generation.

But this of course makes me wonder.. do I need an i7? When I bought my i5, more or less all games were solely single-threaded, but isn't this starting to change? Watchdogs, Wolfenstein etc all have i7 for the "recommended" specs. Secondly, how well would an i7 Haswell handle a pair of 290s in Crossfire compared to an i5?

 

[Techhog]

You'll still be fine for the most part, but an overclocked i7 wouldn't hurt for this kind of system

 

[Skott]

I think you would see a major performance improvement going i7 with a pair of 290x. You can always do the second 290x first just to see how well it does.

 

[KingRaptor]

Regarding your 2nd point: Secondly, how well would an i7 Haswell handle a pair of 290s in Crossfire compared to an i5?

With i7 Haswell (not Haswell-E or Ivy Bridge-E) you would still be limited to a total of 16x PCI-Express 3.0 lanes shared across both cards. Many reviews online suggest that PCI-Express 3.0 at 8x is plenty fast enough for most GPUs at reasonable resolutions. Therefore, unless you're running crazy high resolution (4K+ or 5-screen eyefinity,) you should be fine with an i7 Haswell and two R9 290s.

I think the biggest benefit of going from an i5 Haswell to i7 Haswell would be raw CPU performance increases due to the the i7's faster clockspeed, larger cache, and hyperthreading. This is all at stock performance; I haven't factored in overclocking with an i7's unlocked multiplier.

 

[Mondozei]

You'll still be fine for the most part, but an overclocked i7 wouldn't hurt for this kind of system

That sounds like "not really necessary but nice"

I think you would see a major performance improvement going i7 with a pair of 290x. You can always do the second 290x first just to see how well it does.

And that sounds like "you should probably do it".

As for buying the second 290 first, well, the point of this thread is kind of knowing stuff before I take the plunge. Because if my i5 isn't up to it, I'd rather not spend my money on an i7 and just wait for a faster single GPU instead. Hence this thread.

Regarding your 2nd point: Secondly, how well would an i7 Haswell handle a pair of 290s in Crossfire compared to an i5?

With i7 Haswell (not Haswell-E or Ivy Bridge-E) you would still be limited to a total of 16x PCI-Express 3.0 lanes shared across both cards. Many reviews online suggest that PCI-Express 3.0 at 8x is plenty fast enough for most GPUs at reasonable resolutions. Therefore, unless you're running crazy high resolution (4K+ or 5-screen eyefinity,) you should be fine with an i7 Haswell and two R9 290s.

I think the biggest benefit of going from an i5 Haswell to i7 Haswell would be raw CPU performance increases due to the the i7's faster clockspeed, larger cache, and hyperthreading. This is all at stock performance; I haven't factored in overclocking with an i7's unlocked multiplier.

Well, part of the reason why I'd be getting a second 290 is my eye looking at 4K. I mean I'm getting a 4K monitor once I can find a 100+ Hz one which is a single stream IPS display. Because my Crossfire 290 wouldn't probably be my first dual-GPU setup, since I think you'll more or less need it for 4K for a plenty of years ahead if you want high framerates.

Getting a Haswell-E is kind of out of the question unless the price is sub-500 dollars and even then I'd be skeptical.

But so far I haven't really got a concensus... would it be worth upgrading to a i7 from a new i5?

Divide the answer into two parts. First for my current 1080p gaming, how much of a performance delta would I find for a Crossfire setup of two 290's with an i7 compared to i5? And secondly, how about 4K?

 

[Techhog]

At 1080p, your CPU would definitely be the weak spot in your system. At 4k, the graphics cards are the "bottleneck." That said, the i7 is definitely better for a CF system; I just don't know if it's a big enough difference to justify the cost.

 

[BrightCandle]

Gamegpu.RU test all their games with sli, so most of their CPU tests would be quite representative of the performance differences you might see. I wish they had more recent CPUs but it should give you a good idea what performance benefit for gaming with 2x cards will get you.

 

[toughtrasher]

Lol I was considering getting the Sapphire 290 card Is it good?

Anyway, yeah the i7 would benefit you a lot compared to the i5, and I heard a lot of people pairing the two together and it runs fine.

 

[nurturedhate]

I think the real question is what i5 do you have. If we are talking about a locked down 4440 or 4570 then moving to an i74770k and overclocking to around 4.4 would be an upgrade worth consideration but if we are talking about a 4670k that's already overclocked then I wouldn't upgrade.

 

[Mondozei]

At 1080p, your CPU would definitely be the weak spot in your system. At 4k, the graphics cards are the "bottleneck." That said, the i7 is definitely better for a CF system; I just don't know if it's a big enough difference to justify the cost.

Me neither, hence the thread!

I think the real question is what i5 do you have. If we are talking about a locked down 4440 or 4570 then moving to an i74770k and overclocking to around 4.4 would be an upgrade worth consideration but if we are talking about a 4670k that's already overclocked then I wouldn't upgrade.

I got the i5 4670K, but it is at stock speeds right now(because my system is running really hot, around 80 Celcius at stock speeds at the moment. But that is probably due to too few fans and/or bad CPU cooler(no, I don't have the stock Intel one)).

Lol I was considering getting the Sapphire 290 card Is it good?

The Sapphire 290 is great. I've been using Nvidia since my first PC over 10 years ago, when I was just beginning 7th grade. So this is my first AMD card and it is the most quiet card I've ever used, plus the temperatures are ungodly. Often mid-60s for very demanding games.
But that's a bit off topic

Anyway, yeah the i7 would benefit you a lot compared to the i5, and I heard a lot of people pairing the two together and it runs fine.

Quantify. "A lot" is too imprecise.

 

[Mondozei]

I'm just surprised how difficult it seems to be to get a straight answer. Nobody really seems to know.
I'll just re-iterate this part:

Divide the answer into two parts.
First for my current 1080p gaming, how much of a performance delta would I find for a Crossfire setup of two 290's with an i7 compared to i5?
And secondly, how about 4K?

 

[Techhog]

I got the i5 4670K, but it is at stock speeds right now(because my system is running really hot, around 80 Celcius at stock speeds at the moment. But that is probably due to too few fans and/or bad CPU cooler(no, I don't have the stock Intel one)).

Okay, that changes my opinion slightly. I'd recommend waiting to see what Devil's Canyon offers. If the rumor about the 4790K being 4GHz stock is true, it's worth buying.

 

[Elfear]

I'd just get a good cooler for your i5 and overclock it. There are very few games that take advantage of hyperthreading. I've used both a 4670k@4.6Ghz and a 4770k@4.7Ghz and I couldn't see any difference between the two while gaming.

 

[toyota]

I'd just get a good cooler for your i5 and overclock it. There are very few games that take advantage of hyperthreading. I've used both a 4670k@4.6Ghz and a 4770k@4.7Ghz and I couldn't see any difference between the two while gaming.

for the most part yes but high end multi gpu adds more cpu overhead so an i5 will be tapped out in some cases. and there is a playable difference in Crysis 3 too.

 

[Elfear]

for the most part yes but high end multi gpu adds more cpu overhead so an i5 will be tapped out in some cases. and there is a playable difference in Crysis 3 too.

Agreed. There are a few games where you'll see a difference. Crysis 3 and Stracraft II off the top of my head. I never played either but have read some reviews.

 

[Mondozei]

I'd just get a good cooler for your i5 and overclock it. There are very few games that take advantage of hyperthreading. I've used both a 4670k@4.6Ghz and a 4770k@4.7Ghz and I couldn't see any difference between the two while gaming.

Thanks for the informative comment, i.e. based in real life useage.

My two counter-arguments:

1. While it was certainly true that the benefits of an i7 over an i5 was relatively small previously, the same may now change. There are many games coming up where they recommend an i7. Wolfenstein, Watchdogs. Even Star Citizen. It remains to be seen for games that are just about to be released like Wolfenstein/Watchdogs, if the performance delta for an i7 is really significant.

I bought an i5 last year in large part because the fact that I recognized the fact that for a single GPU, an i7 would be a waste of money by and large for the vast majority of gaming. However, the tide seem to be slowly turning, as the newer games come out and more and more are recommending an i7. Too early to tell precisely just yet, which is why I'm hoping some sites will do CPU comparisons when Watchdogs/Wolfenstein come out.

2. I'd just remind you that I'd be using Crossfire, which is why I was a bit surprised why you left out your GPU setup in your comment. Did you use a single GPU or several? And as Toyota stated, once you use high-end GPUs, the performance delta between an i7 and i5 increases, but my question is by how much?

Nobody has still been able to quantify that question or even give a guesstimate. I'm actually a bit surprised by this.

 

[toughtrasher]

Just get the 290 bro, you know well it's going to do you better in the future for these games.

 

[MrPickins]

I'd just get a good cooler for your i5 and overclock it.

Best advice in the thread.

Even if you go with an i7 eventually, you'll want to overclock it for best performance, so the cooler purchase is a no-brainer.

And that will allow you to do real world tests on how well your OC'ed i5 pairs with a second 290x, using the games that you actually play.

 

[2is]

I would certainly not spend the money to upgrade an i5 to an i7 of the same generation.

 

[BrightCandle]

No I wouldn't pay for i5 to i7, the performance difference would be undetectably low. Most of the time it would be nothing and in the few occasions it was fully using hyperthreading you would be looking at 20% maximum, which isnt going to make something not working well enough into working.

 

[nurturedhate]

I would certainly not spend the money to upgrade an i5 to an i7 of the same generation.

Especially considering the overclock lottery. You could be sitting on a 4.6-4.7 i5 and then "upgrade" to an i7 that only does 4.2.

 

[crashtech]

I would OC the 4670K as well. A big aftermarket cooling setup of some sort would be a decent upgrade that should be pretty useful moving forward.

Reason being is that not all games benefit from HT, but they ALL benefit from higher clock speeds.

 

[Mondozei]

Well, I'd still like to see any quantifiable data when comparing i5 and i7 when the system has two high-end GPUs.
There still isn't any of that so far, and I'm convinced by numbers, not opinions(or rather: opinions backed up by numbers).
And until I see any, not making any real decision.

P.S. my cooler is a Cooler Master 212 Evo. Not the best out there, but surely it should be doing better than ~75-78 C at 3.4 GHz stock speeds under load?
My case may just be really warm. I just have two Noctua fans and both are optimized for silent operation. Not sure how much a new cooler would solve in such an environment.

 

[Mondozei]

I contacted Ryan Smith and asked specifically about the 290s and here's what he had to say:

[FONT=Calibri,sans-serif]Desktop i7 processors are faster than the top tier i5 processors, but not immensely so. Like so many other performance questions the exact performance difference depends on the workload in question, but it boils down to a few percent from higher [FONT=Calibri,sans-serif]clockspeeds[/FONT][FONT=Calibri,sans-serif], a few percent from more cache, and a few percent from [/FONT][FONT=Calibri,sans-serif]Hyperthreading[/FONT][FONT=Calibri,sans-serif]. It’s not the same kind of massive jump that we see from i3 to i5 because the core count hasn’t changed.[/FONT][/FONT]

[FONT=Calibri,sans-serif]If you can afford to drop the $800+ on a pair of 290s, then I’d suggest going with an i7 because dual GPUs leaves you at greater risk of being CPU bottlenecked. In those scenarios the i7 will be 10-15% faster, which won’t be a massive difference but at the same time is not insignificant at a time when CPU performance gains are harder and harder to get.[/FONT]

[FONT=Calibri,sans-serif]Also, if you haven’t already, I’d suggest looking at our recent [FONT=Calibri,sans-serif]Haswell[/FONT][FONT=Calibri,sans-serif] refresh review: [/FONT][FONT=Calibri,sans-serif]http://www.anandtech.com/show/7963/the-intel-haswell-refresh-review-core-i7-4790-i5-4690-and-i3-4360-tested[/FONT][FONT=Calibri,sans-serif]. We cover both traditional desktop usage and gaming, so it should give you [/FONT][FONT=Calibri,sans-serif]some[/FONT][FONT=Calibri,sans-serif] idea of what to expect.[/FONT][/FONT]

[FONT=Calibri,sans-serif]The i7-4790 vs. i5-4690 is a great example of the performance difference between an i5 and an i7. If you’re CPU bottlenecked, it can be 10-15% faster. If you’re not, then it doesn’t do anything for you. [/FONT]

[FONT=Calibri,sans-serif]Note that your likelihood of being CPU bottlenecked also depends on the monitor. Long story short, higher [FONT=Calibri,sans-serif]framerates[/FONT][FONT=Calibri,sans-serif] require faster CPUs, but not higher resolutions. You’re much more likely to be CPU bottlenecked on the 1440p 120Hz monitor than you are a 4K 60Hz monitor due to this, as you’ve doubled the number of frames the CPU needs to serve up. If you expect to sustain 120fps then you’re definitely going to want the i7, as it will have the best shot.[/FONT][/FONT]

The dual-GTX 770 LE(or 7970s for AMD) used in their Haswell Refresh review are not quite high-end cards but they are close.

And it seems like I finally got a number to expect for high-end GPUs, 10-15%. So not that hugely significant but certainly notable in an era with small CPU incremental IPC increases. I got a 144 Hz monitor right now for 1080p but mentioned that I'm thinking about either going 4K or 120 Hz 1440p when that comes out in greater numbers.

As expected by a senior GPU editor, Mr Smith gave a very informed answer. I'm still not totally sold if it's worth it, but considering that I prize my high frame rates a lot, meaning that I'd be more likely to jump to 1440p at 120 Hz than going to 4K in the immediate future, the i7 just got a boost in my eyes. At the same time, low IPC increases notwithstanding, 10-15% is not huge. I thought I'd be bottlenecked by 20-30% or so.

Well, the thread is more or less over as I did get the answer, only via email

It could serve as a reference for people in the future with similar concerns, since it seemed to be pretty hard to get a straight, data-driven answer from people. (I.e. nobody really seemed to know for sure what the performance delta was).

 

[frozentundra123456]

Just a judgement call, but I think if you are using a high end set up, and starting from scratch it is a good call to go with an i7. If you are spending 800 dollars or so on dual gpus and all the power consumption that goes along with it, an extra hundred dollars for a cpu is not that significant. But if one has an i5 already, it becomes more difficult to justify switching that out for an i7. I suppose you could buy an i7 and either sell the i5 or use it for another system. Hopefully, within a couple of weeks we will have benchmarks for Wolfenstein and Watchdogs to make the situation a bit clearer.