did you create keyclone commands to launch your wows? (it makes life a lot easier)

when you do that, make sure to set the maxfpsbk and maxfps fields. anything over 50 fps is overkill (the avg human eye sees about 42fps). the maxfpsbk is the number of frames your wow will try to get when it is not active. this saves your cpu and gpu loads of headaches.

personally, i 5-box on 2 screens @ 1680x1050 and get 15/42 (maxfpsbk 15 maxfps 42) almost constantly. (cpu stays around 50%)

also... the fps does depend on what it is trying to be rendered. if you have something a bit more complex walking around, it might reduce the fps until it is out of frame.