try using the sensitivity the max that you can go and try to get used to them.....because then you can move around faster and aim faster....its a little hard at first but youll eventually get used to it =]
I set the bounding box to it's smallest possible size, and change the horizontal look speed and aiming sensitivity one step higher pretty much every time I play. Once it gets too sensitive, I'll dial it back. I leave vertical look speed pretty much where it is.
They work okay for me where they are now, but I'm always betting more sensitive will be better.
I put the aiming sensitivity all the way up, make the aiming box thing a little bigger, and the left and right and up and down speed almost all the way up (like, if i put up 2 more times it would be all the way up). That hits the sweet spot.