http://www.funender.com/quake/mouse/index.html
According to this if you use a really high dpi with a low in game sens you could experience significiant negative accel.
For example you use 1600 dpi @1920 x 1080, 0.5 in game sens, 200 fps.
cm/360 = 51.9
in/360 = 20.4
Useful DPI = 295
Accel = 0
Neg. Accel at Max speed of 3.048m/s
Change only the DPI to 800 and the sens to 1 and you get.
cm/360 = 51.9
in/360 = 20.4
Useful DPI = 295
Accel = 0
Neg. Accel at Max speed of 6.096m/s
Taking this to an extreme at set a mouse to the DPI of 12000 with 0.07 ingame sens and you get
cm/360 = 49.4
in/360 = 19.4
Useful DPI = 309
Accel = 0
Neg. Accel at Max speed of 0.4064m/s
Which would make playing really inconsistent.