The other thing is that gaming with 2 displays is about the dumbest thing you can do - the center of the screen, which is where you want to be focusing most of your attention, will be split in two, with large frames in between. That could get REAL confusing, real fast.
This is not true for some games. For example, for supreme commander 2, you can have one screen be the main game screen and the other be the strategy map. It really depends on the game supporting 2 monitors. I run supreme commander 2 on 2 screens using one GTX 580.