I recently replaced my MSI 770-G45 with the ASRock M3A785GXH128M, because it was able to do x8/x8 with the PCI Express slots. I have two HD 5850s, and when I installed them into my 770-G45, the performance with twin cards was about the same and sometimes less than single card. I created a thread about that issue and the conclusion was that the x4 operation slot of the second card was slowing the whole thing down, and that I needed at least x8/x8 to run CrossFire properly. That is why I got the ASRock M3A785GXH128M, hoping that I would be able to actually benefit from two cards when I have x8/x8 operation PCI Express slots. But to my astonishment, the performance was the same as single card as well, maybe even not as good. So what exactly is going on here? I made sure to do the manual switch to x8/x8 mode with this motherboard, but it still does not yield any performance benefits.
(I tested the performance in Crysis Warhead and Bad Company 2)
GPU-Z indicates that there are 2 GPUs enabled, and I've tested the performance in 3D Mark Vantage, the score with single card was around 15,000, now with both cards it's 22,000. But that seems to be the only place I have seen a performance increase.
I run at 1280x1024 resolution due to monitor, but I still don't think I should see a performance drop, if not any increase.