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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High level PvP'ers will tell you that if you're sniping you should use anywhere from 2-5, and if you're shottgunning you should use anywhere from 5-8. I used to use 10 only, but i've learned that 5-7 helps my aim and accuracy tremendously.