Naga's good but the dpi will be too high for FPS.
A lot of people go with around 1600 dpi, but even that's too squirly (not fast, just jittery when testing in MS Paint). I use 600 or 800 depending, and raise the in-game sensitivity. You can get it to be just as fast, but without losing accuracy.
Also disable Windows mouse acceleration (if you're getting performance hardware you might as well tune the software too, so that you're getting 100% benefit from the good hw. Otherwise you have software playing a major role in how your hardware works). Most of these adjustments are only noticed in FPS or games where quick accurate mouse movements matter.
