Don't even get me started.
Who cares about what sensitivity pros play on? It's a game and it's totally up to personal preference. One sensitivity isn't better than another, and there is no "golden" sensitivity. I started playing Halo 3 on 3, then went up to 10 for while. I didn't like it, and went down to 5. Then I discovered that I liked 1 for a while. Now I'm on 8. Preferences change, but across all the sensitivities I've played on, my individual and team skills remained unaffected. It's just a matter of getting used to one over another.