I usually play crucible and use snipers in my special slot.
I use kontrol freeks, a long one on my aiming stick.
Also I play on a 24" monitor
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2-4 is what the best players play with. Being able to turn around fast means nothing, as any competent player will kill you regardless if he gets a free shot in your back. Precision is what matters. But keep in mind you have to find your own sensitivity. It takes like a week or more to get used to a new sensitivity, so play around a lot!