I play on 4 with reg guns and 8 with a sniper. As it is named, 4 is HIGH, many people might find it slow but when you turn around running it makes it really good, my friends tought that I played on 7 till they went home and played there. And 8 because usually when I'm snipping I'm just messing around and quickscoping
EDIT: when you play on a bad connection like me every single bullet counts so I try to almost never miss, but when I'm playing on a friend's house that always pulls host I go up to 7 sometimes :|