The PCI-E controller will only have so many lanes connecting to the devices. The maximum amount of lanes any one PCI-E peripheral can have is 16 (x16). A single graphics card is x16 capable and will take up the full 16 lanes for maximum bandwidth.
Two graphics cards will have to share 16 lanes between them, hence x8,x8, despite the reduced bandwidth the processing power of 2 graphics cards improves performance.
the x8 links will not decrease performance that much, 2 x 5870's in x8/x8 link loses about 4% of the performance of x16/x16. The only cards to be affected greatly are the dual gpu cards (as each gpu is only getting x8/x8 in one x16 slot so x8 would become x4/x4)
seems like i dont need to worry then
there will be a small difference although if u r getting 50 fps on x16 x16 lanes
u will get 48 or maybe 45
there is not much detectable difference between 48 and 50
thnx for the support
I had a little convo in another thread about it. Looks like it really depends on the GPU. Some midrange ones you won't see any difference. The only reason the 5870 is 4% faster on a 16x lane is that it's total output is just 4% more than an 8x lane can deal with. Possibly a 5970 would see closer to, oh, 10 or 15% drop in performance. But then going the other way, a 5770 might not see any change.