Can't say I know much about this. I use a cheap mouse that claims to have 1000dpi but I don't actually believe it is true.
I turn off mouse acceleration in the operating system (not completely sure it has an effect anyway) and have the UT mouse sensitivity set to 2.5. I came to this sensitivity setting years back mainly because it allowed me to turn 540 degrees when using the full width of my old standard size mouse pad (at fov 106.26). I also have mouse smoothing disabled in UT. I used these same settings on v436 and now v469b without any difference.
Others here have more knowledge of the various settings than I do. Add some specifics and you might get more answers. What mouse settings are you using both for the operating system and UT and which UT version are you currently using?
Edit: What resolution is your monitor? I'm using 2560x1440 for UT.