Crossfire/surround question - running on 8x/8x pci board

[Jared701]

I just purchased 3 1080p monitors for an eyefinity or surround setup.
I currently have a P5Q-E motherboard (775 P45 chipset) It supports crossfire but only at 8x/8x pcix. I found this http://www.hardocp.com/article/2010/08/25/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x4x4/ At least with the 480s in SLI there was less than a 10% difference between running 16x16 and 8x8. I found another article that said it was 5% or less difference in 6870s but I can't seem to find the article now.

The [H] article was looking at 3x 1200p monitors so my resolution will be slightly smaller. I'm wondering if 2 6970s would experience the same 10% or less difference that I've found in the articles? I honestly don't want to put in the money for a complete system upgrade right now. I have a Q9550 which is running @ 3.65 stable and have seen from game benchmarks that I wouldn't gain much from going to sandy bridge.

From what I've seen, going crossfire at a 3 monitor resolution can give HUGE gains in fps. I'm just wanting to make sure that my setup would not be wasted due to running them at 8x pciexpress. Can anyone confirm if my board really can only do 8x8? For one card it is able to do 16x.

I've read about the sound coming from a crossfire setup but have also read that if you leave space between the cards that is diminished. I looked at my board and should at least have one pci slot of space between the 2 cards. I'm using a case with good airflow and can mount a fan on the side of the case blowing right between the cards so that should not be an issue.

Here is my system specs if that makes a difference
P5Q-E mb
Q9550 cpu @ 3.65
8 gigs of ram
2 hd (no ssd yet )
1 dvd rom
BFG ES 800w power supply
currently nvidia 260 gtx
I asked in the power supply forum and they said my power should be fine but wanted to include that here in case that may be wrong.

Any help would be appreciated.

 

[Tsumi]

You might be cutting it a little close with the power supply, but you should be perfectly fine.

The 6970 is only somewhat more powerful than the 480s, so you should see similar performance decreases as with the 480s. I wouldn't worry about it in my opinion, and as was stated multiple times in the article, they were unable to feel any difference in gaming <--- most important and relevant part. As long as there seems to be no effect in gaming performance, it doesn't matter what the hard numbers come out to be.

Also, it depends on the games you play. Some games require high PCI-E bandwidth, which leads you to the performance decreases you see. Some games are more dependent on GPU power, so there is absolutely no performance decrease.

 

[Jared701]

You might be cutting it a little close with the power supply, but you should be perfectly fine.

The 6970 is only somewhat more powerful than the 480s, so you should see similar performance decreases as with the 480s. I wouldn't worry about it in my opinion, and as was stated multiple times in the article, they were unable to feel any difference in gaming <--- most important and relevant part. As long as there seems to be no effect in gaming performance, it doesn't matter what the hard numbers come out to be.

Also, it depends on the games you play. Some games require high PCI-E bandwidth, which leads you to the performance decreases you see. Some games are more dependent on GPU power, so there is absolutely no performance decrease.

The article did make me optimistic that I would be able to do it. The other reviews I've seen stating that at this resolution crossfire is almost 100% increase in the fps make it hard to not consider adding another to get decent performance in more demanding games. I remember getting 2x cards to sli back when oblivion came out that only offered like a 15% increase in the fps.... total waste at that point.

 

[samuelmorris]

I'm going to be running 6970s on 8/8x, I have no issues with doing so whatsoever. It it didn't bottleneck 4 GPUs last gen [4870X2 quadCF] it almost certainly won't bottleneck two this gen. I imagine the GTX480 is every bit as reliant on bandwidth as 6970s, if it makes no difference to them, you should be fine.
Crossfire typically scales 95% with the HD6 series. It's always worthwhile on 8x/8x, it's even worthwhile on 8x/4x.