Software sensitivity options usually just modify the movement factor, i.e. taking input from the mouse and multiplying or dividing input values by the modifier value, so it's all very much framerate dependent. If you use the drivers to configure sensitivity it may increase, or decrease DPI, depending on the mouse/driver. However the IME3.0 is awesome without any special drivers, just plug and play/frag. In fact I'd say it's better without the 'proper' drivers. mrsobvious had a good review up there, might not have noticed because he can't post links yet, so I'll reiterate it for him:
http://hardware.gotfrag.com/portal/story/34387/
I know I'm starting to sound a bit like a Microsoft sales rep. (ironically I also love this mouse because it also 'just work's in Linux), or a bit of a fanboy, but I've yet to find one to rival it in all my many years of computing.