Most top players use sensitivities around default since you can actually control your aim and hit a person with a decent strafe. I think 1-2 of the top crucible guys on Xbone play above 7 but that's it. Most of the people saying 10 on here probably aren't that great at crucible. No matter what they say, you CANNOT have absolute control over your aim at those levels like you can at a sensible sensitivity. Against good players a high sensitivity will leave you twitching your aim all over the place trying to deal with a strafe. There are always exceptions, but if anyone saying 10 sens carries over a 2.0 k/d in crucible I'd be surprised.