I am not sure what role sensitivity plays, but if you want to change your sensitivity big time use the in-game setting. Type sensitivity at the console to see your current setting. The default is 10.
Many people find they aim better with lower sensitivity, but turning a full 180, etc. is slower, so it very well could have some impact on strafing.
I think Haze says he uses sensitivity 4 or something, and several others I have asked use a setting between 4-8.
As for jumping I max at about 52 or so just going on level ground, with fairly good mouse movement, so in the same boat as you.
At times what you may be experiencing is they get a faster start through circle jumping, therefore getting ahead of you.
Then again...some do seem incredibly fast.