Another multi-monitor, dual-gpu, mobo PCI-E setup question

[Raswan]

So I'm toying with the idea of adding adding a couple of monitors in order to achieve an eyefinity setup, and I want to make sure I understand how xfire works with what hardware I've got. I don't have an unlimited budget, but I'm willing to spend some money.

Current setup:
Gigabyte P55A-UD3 rev 2.0
i5-760 stock
Sapphire 5870 1GB
Gskill 1333 RAM 16GB
Asus VE278Q 27-inch 2ms monitor

1. From what I can gather, the motherboard absolutely supports xfire. From Gigabyte's support site:

1 x PCI Express x16 slot, running at x16 (PCIEX16) (The PCIEX16 slot conforms to PCI Express 2.0 standard.)
1 x PCI Express x16 slot, running at x4 (PCIEX4)
2 x PCI Express x1 slots
3 x PCI slots

2. Yet Gigabyte's website notes that, "When SATA3 / USB 3.0 (Marvell 9128 /NEC USB 3.0 Controllers) work at turbo mode, 1st PCIE x16 will work at x8 speed." I don't know what engages the "turbo mode," but am using the SATA slots.

(Preliminary question: is my 5870 hamstrung right now @x8 by my sata/usb 3.0 usage and I don't even know it? This is something I need to know like right now.)

3. So, my initial plan was to grab two more of those Asus 27-inchers, flip them vertically, and go nuts at whatever resolution would look sweetest (5760x?). In order to do this, I see three options: either I need another 5870, two of something else, or, alternatively, a single-card solution (don't know that there is anything capable of this--the 7970 maybe? I'm a little out on the gpu literature of the last 6 months, having upgraded a year and a half ago).

Does my mobo support a reasonable xfire setup, or are the limitations of that second PCI-E slot going to kill me? If not, what would be the best of the three options above (I realize I'll have to get the 5870 used from someone)? Is this all a pipe dream?

Thanks guys. I really appreciate the help in wading through all of this.

 

[fffblackmage]

I don't think CFX is worth doing on that setup. The first PCIe slot running on 8 lanes isn't a problem (perf. loss of only a few %). However, the second slot with only 4 lanes will be a bottleneck.

 

[Ieat]

1. Honestly your current system isn't well suited for multi gpu eyefinity or nvidia surround. Pcie x8 is fine but Pcie x4 will bottleneck your gpus in some games. It really depends on the game. Some games will hardly be effected at all while others may take a noticeable hit.

2. Turbo mode would probably be attaching usb 3 or sata 3 devices. I don't know if you can turn turbo mode off or it auto senses. Probably need to read your owner's manual for that. But you can tell what X your 5870 is currently running at by downloading gpu-z.

3. If your set on keeping the motherboard and still want to do eyefinity I would suggest getting a single 7970 or 7950 out of those 3 options. Getting another 5870 would leave you vram starved at eyefinity resolutions and you would still have the x4 problem. Getting 2 different cards will still leave you with x4 issue.

 

[Raswan]

I don't think CFX is worth doing on that setup. The first PCIe slot running on 8 lanes isn't a problem (perf. loss of only a few %). However, the second slot with only 4 lanes will be a bottleneck.

Thanks for the assessment blackmage. For my future reference, do you know of a convenient and easy to understand reference guide that can give me exact numbers on the performance difference between 8 and 16 lanes? It has become apparent that my knowledge of how PCI-E works is weak-ass.

 

[Raswan]

1. Honestly your current system isn't well suited for multi gpu eyefinity or nvidia surround. Pcie x8 is fine but Pcie x4 will bottleneck your gpus in some games. It really depends on the game. Some games will hardly be effected at all while others may take a noticeable hit.

2. Turbo mode would probably be attaching usb 3 or sata 3 devices. I don't know if you can turn turbo mode off or it auto senses. Probably need to read your owner's manual for that. But you can tell what X your 5870 is currently running at by downloading gpu-z.

3. If your set on keeping the motherboard and still want to do eyefinity I would suggest getting a single 7970 or 7950 out of those 3 options. Getting another 5870 would leave you vram starved at eyefinity resolutions and you would still have the x4 problem. Getting 2 different cards will still leave you with x4 issue.

I have toyed with the idea of a different mobo, but figured that would add at least another 175$ to the total upgrade cost. Add that to another 5870 (the cheapest option), 2 more monitors at ~300$ each, ~100$ or whatever for mounts, and I'm north of a grand to satisfy the upgrade bug. At that point, seems smarter just to turn my 46-inch Aquos into my main monitor and save the money for a massive upgrade in another year or two when that i5-760 is looking anemic.

I'll run gpuz and see what it says. This is definitely something I should have known about when buying that board; live and learn, I suppose.

 

[Ieat]

If you don't need sata 3 or usb 3 and aren't in a hurry I would stalk ebay for a used p55 with x8/x8. They can usually be had for $70 to $80 shipped. I got an Asus P7p55d Pro for $53 shipped but that's abnormally low. You could probably sell your board after finding one and only pay $10 to $20 for the swap.

If you do decide to get a new board I would sell the 5870 and get 2 gtx 560 2gb or 2 6950 2gb. 1 gb of vram just isn't enough for dual cards and 3 monitors. For example I tried gtx 560 ti 1gb in sli and then switched to gtx 460 2gb in sli and I could actually play games at higher settings with the 460s even though 560 ti's are suppose to be about 25% faster then 460's.

 

[Raswan]

If you don't need sata 3 or usb 3 and aren't in a hurry I would stalk ebay for a used p55 with x8/x8. They can usually be had for $70 to $80 shipped. I got an Asus P7p55d Pro for $53 shipped but that's abnormally low. You could probably sell your board after finding one and only pay $10 to $20 for the swap.

If you do decide to get a new board I would sell the 5870 and get 2 gtx 560 2gb or 2 6950 2gb. 1 gb of vram just isn't enough for dual cards and 3 monitors. For example I tried gtx 560 ti 1gb in sli and then switched to gtx 460 2gb in sli and I could actually play games at higher settings with the 460s even though 560 ti's are suppose to be about 25% faster then 460's.

Thank Ieat. Good advice. I'll keep an eye on ebay and see if something crops up. Might be worth it.

 

[Meaker10]

Just to point out that second slot is 4x gen1 (same as 2x gen2) because it's using the south bridge lanes.

 

[fffblackmage]

Thanks for the assessment blackmage. For my future reference, do you know of a convenient and easy to understand reference guide that can give me exact numbers on the performance difference between 8 and 16 lanes? It has become apparent that my knowledge of how PCI-E works is weak-ass.

Here is a good article on PCIe bandwidth and how it affects gaming performance.
The Radeon HD 7970 Reprise: PCIe Bandwidth, Overclocking, & The State Of Anti-Aliasing

 

[Raswan]

Here is a good article on PCIe bandwidth and how it affects gaming performance.
The Radeon HD 7970 Reprise: PCIe Bandwidth, Overclocking, & The State Of Anti-Aliasing

Cool. Thanks!