Currently I play on 8 as I feel that it is where I am most accurate. I can play on all the way up to 14 in Black Ops 2 and 10 in all previous COD Titles. At 14 however whenever I get into situations that require me to be very precise turns and movements sometimes I just barely turn too much and wind up missing my target. And in Hardcore Kill Confirmed that little aim problem is what will be the deciding factor in a confirm for you or a confirm for the enemy team.