In case anybody is wondering if dual PCI-E 2.0 8x is ok for crossfire performance. I have a Asus P8P67 PRO, 2600K, 8GB memory, so max PCI-E 2.0 8x for crossfire. At first everything seems to be ok, heaven benchmark, metro last light, some other games. All seem to scale perfectly. But still now and then i've had these slowdowns.... it reminded me of the AGP days where it would happen if the gpu memory wasn't big enough and it started swapping textures over the AGP bus. The more i tested the more it seemed the dual PCI-E 2.0 8x speeds where limiting the performance. The final test which convinced me this was the case was Farcry3. With crossfire (dual PCI-E 2.0 8x) there where BIG slowdowns, especially looking up the sky. With crossfire disabled but still with (PCI-E 2.0 8x) performance already a lot better, but still a slowdown is noticable. (again look at the sky) Finally i completely removed the second GPU so the PCI-E 2.0 @16x again. Now the performance is good again. I am not sure why this is happening, looking at the sky in farcry3 there is nothing to render... but still. This is all tested without vsync and the 13.12 drivers (later also with the 14.1 beta driver but its the same). Can someone with crossfire check if looking at the sky in farcry3 causes a slowdown? If yes/no what config you have?