I played on 3 in H3, but due to the slightly different aiming mechanic in Reach I switched up to 4. My fine aim for DMR battles/Sniping is still fine, but when I tried to play on 3 in Reach the quick sweeps were just too slow. It made turning quickly and whip noscopes too difficult. I've found my home with 4 now, works great for me.
I hate 10 honestly because it is too fast. Since your on 10, I would really like to see your gameplay. You probably fail at no-scoping unless you are really good at it that fast. I play 4 or 5. Sometimes 2
I've learned to adjust my thumbs for fine movements because I've played with the sensitivity up so high for so long. I like the high sensitivity in close quarters combat because it allows me to react a bit quicker to someone that got behind me. I occasionally get a no-scope or 2, but i was never all that great with them to begin with. I can't play with anything below 5 now though. It feels like I'm moving through molasses. EDIT: I just saved a vid of me using a sniper in a match. when I get the right cords for my capture card, i'll upload it to youtube so you can make fun of my terrible gameplay.
I think I'll be moving back down to six, from seven. Maybe to five. I voted seven, though. However, I find I'm not getting headshots as easily, so I'll boogie on down to six today.
I roll 7. I stayed on the default for a while, but because I was getting assassinated too often I threw it up to 7. I snipe all the time and make plenty of head shots. I honestly felt the high sensitivity increased sniping capabilities.
I play on 5. Because 5=high in GoW2. It's also helped me bring my k/d back from the grave, to a 1.5. I can't understand why it was as low as .9 in the first place...
10. Considering the sensitivity is much.. softer.. than in CoD it was rather easy to accommodate to playing on 10. edit; Dead-Thread Revival Fail.