Ehh, I can't help it. Not even college can get me away from here, but I'm not getting myself involved in anything stupid on the forums anymore. Good lesson learned a bad way :P
I'd say 5 to 6 cm/360. Ideally, one swipe of the mouse across the mouse pad should be as close to one full rotation as possible, no more or less. I know one of the Omnis said that at some point, and that has helped my game a bit more.