What i have to say on this matter is that you dont need to play on a high sensitivity to be good, and now people think that you have to do 360's and no scope your opponents to be good, but remember that this is only to show off.
The use of sensitivity is to give you the accuracy and reflexes you need.
In my case, when i started playing, my sensitivity was on 2. I quickly felt the need to increase it because i could not turn around fast enough when i had to, for example, defend myself against somebody in my back, or in most CQC situations when i had more than one target. I kept playing on 4 for a while. I tought this was the perfect setup because i felt i could turn around fast without impairing my accuracy. Then i realized, with the experience of sniping against friends in sniper battles or simply in public matches, that i could not drag my scope fast enough to keep up with fast moving targets or in CQC situations. I raised it to 7 only for functional sniping purposes, and i decided to keep it like this so i would'nt be confused when using assaults or smgs. It made me realize i could now switch between targets while still aiming down sights with any gun, so it proved very useful.
In the end what i want to say is that you need to adjust your sensitivity to suit your needs, and doing 360's and that kind of fantasy is purely optional and does not relate too much in KILLING your enemy, and staying alive, which requires more strategy and teamwork than plain simple thumbs skills...remember that kids! :p