I've had issues with trying to run WoW on 3 big monitors using 2 8800 GTXs. It seems like PCI-E bus contention is causing framerate slowdowns when I use all 3 monitors. Currently I can only get a smooth 60 fps on my main if I also run 2/4 clones on the same 30" monitor. Ymmv.

Adding 3rd video card = *worse* performance?