here's something else that can radically improve your performance:
wow in-game graphic detail macros (helps performance)

i recommend setting all clones to low detail.. and only bring one up (your main/active) to medium or high

of course, besides fps and level of detail... the pure number of pixels you are trying to push is a factor.
don't run in 1600x1200x2 mode... 1280x1024x2 lessens the load on the gpu/cpu radically

1600x1200x2 == 3.8 million pixels / frame
1280x1024x2 == 2.6 million pixels / frame

a 50% savings...