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7950 Crossfire with 4x PCI-e

Smartazz

Diamond Member
Dec 29, 2005
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Hi all, I currently have one Sapphire 7950 clocked at 1100MHz core and 1375MHz memory hooked up to a 2560 by 1440 Achieva Shimian. I love the setup but I feel as though one card isn't enough to hold 60fps in all my games with the AA turned up. This: http://www.newegg.com/Product/Product.aspx?Item=N82E16813138344&Tpk=tz68k+ is my motherboard which supports Crossfire but the second card would only be running at 4x speed. Is that going to slow things down a lot and is a 620W Seasonic going to be enough even if I lower the clock speeds to say 1GHz. Thanks in advance.
 

Smartazz

Diamond Member
Dec 29, 2005
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What is the consensus on this? With the price of the Geforce Titan being so high, I think that getting another 7950 is the way forward. Is a 4x PCI-E slot for the second card going to be a problem?
 

CurrentlyPissed

Senior member
Feb 14, 2013
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What is the consensus on this? With the price of the Geforce Titan being so high, I think that getting another 7950 is the way forward. Is a 4x PCI-E slot for the second card going to be a problem?
PCI-e 2.0, or 3.0? 2.0 4x is a bit slow. It'll work but you will likely hit bandwidth limitations, if 3.0. Then it won't be as bad.

Sorry just read your specs, so yes it's 2.0. You will see bandwidth limitations, but nothing that won't make it a worthwhile addition.
 
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Termie

Diamond Member
Aug 17, 2005
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What is the consensus on this? With the price of the Geforce Titan being so high, I think that getting another 7950 is the way forward. Is a 4x PCI-E slot for the second card going to be a problem?
The consensus? How about the benchmarks:
http://www.anandtech.com/show/5458/the-radeon-hd-7970-reprise-pcie-bandwidth-overclocking-and-msaa

A 7970 (or in your case an OC'd 7950) loses between 0% and 25% being run at PCIe 3.0 x2 (equivalent to your PCIe 2.0 x4). With newer games, this will just become worse.

I wouldn't do it. You're probably hoping to increase performance by ~80% with crossfire but you'll see more like 60%.

And 620w is definitely cutting it very close for OC'd HD7950 crossfire. An HD7970 crossfire set running at stock pulls up to 375w in Crysis 2, and that's just the cards: http://www.techpowerup.com/reviews/ASUS/HD_7970_CrossFire/22.html

Add in your OC'd CPU and the rest of the rig, and you're likely at 550w. Too much for a 620w PSU in my opinion.
 

Smartazz

Diamond Member
Dec 29, 2005
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The consensus? How about the benchmarks:
http://www.anandtech.com/show/5458/the-radeon-hd-7970-reprise-pcie-bandwidth-overclocking-and-msaa

A 7970 (or in your case an OC'd 7950) loses between 0% and 25% being run at PCIe 3.0 x2 (equivalent to your PCIe 2.0 x4). With newer games, this will just become worse.

I wouldn't do it. You're probably hoping to increase performance by ~80% with crossfire but you'll see more like 60%.

And 620w is definitely cutting it very close for OC'd HD7950 crossfire. An HD7970 crossfire set running at stock pulls up to 375w in Crysis 2, and that's just the cards: http://www.techpowerup.com/reviews/ASUS/HD_7970_CrossFire/22.html

Add in your OC'd CPU and the rest of the rig, and you're likely at 550w. Too much for a 620w PSU in my opinion.
Darn, that's not good. I guess this is a bad upgrade path then. One 7950 doesn't quite cut it.
 

aaksheytalwar

Diamond Member
Feb 17, 2012
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You would need to upgrade the Mobo and the psu as well.

Total cost would be an additional $150-200 compared to what you planned. And then you would deal with ms. IMO either do nvidia sli if you are desperate or stick to single gpu solutions.
 

Smartazz

Diamond Member
Dec 29, 2005
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You would need to upgrade the Mobo and the psu as well.

Total cost would be an additional $150-200 compared to what you planned. And then you would deal with ms. IMO either do nvidia sli if you are desperate or stick to single gpu solutions.
I'm thinking of selling my 7950 and buying a good 4gb gtx 680. This way I can make a Hackintosh and get a more powerful GPU. Is a 4gb 680 worth the price premium over the 2gb?
 

hjalti8

Member
Apr 9, 2012
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I'm thinking of selling my 7950 and buying a good 4gb gtx 680. This way I can make a Hackintosh and get a more powerful GPU. Is a 4gb 680 worth the price premium over the 2gb?
why? a 7950@1100mhz is faster than a stock gtx680 at that resolution:|
 

chimaxi83

Diamond Member
May 18, 2003
5,650
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I'm thinking of selling my 7950 and buying a good 4gb gtx 680. This way I can make a Hackintosh and get a more powerful GPU. Is a 4gb 680 worth the price premium over the 2gb?
A 4 GB card isn't worth it over a 2 GB card unless you're going multi GPU and high resolution. A single 4 GB card offers absolutely nothing over a single 2 GB card.
 

Smartazz

Diamond Member
Dec 29, 2005
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I want to get Haswell this summer. Would it make sense to get a 2nd 7950 now and use it with a better motherboard and Haswell when it's released.
 

Termie

Diamond Member
Aug 17, 2005
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I want to get Haswell this summer. Would it make sense to get a 2nd 7950 now and use it with a better motherboard and Haswell when it's released.
That's would be fine, but I guess the real question is whether you need that second 7950 now or you can wait until later, when you have more games that can take advantage of it, along with the platform to make the most of it.

Playing every game at 60fps is not really necessary. The only game I've found where that type of framerate actually matters is BF3 multiplayer. I play all my single-player games at 40-60fps, and enjoy them a lot. Only in the past three months have any games come out that I couldn't lock at 60fps on my GTX670 at 1440p. Part of me is tempted to buy a second card, but it just wouldn't be a very rational decision. It will take several games diving below 30fps to really push me over the edge. I'm sure that day will come, but I think it's premature to say an OC'd 7950 or 670 can't play at 1440p.
 

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