I used to play with sens around 2 when I started out. Later I changed to 3.21 when I started playing a lot of soldier. Sniper and soldier are my two most played classes and I am too lazy to adjust sens for each. So I put it in the middle =]
Honestly, one can get used to anything. Now with a higher sens, I have to be able to be really precise, predict and lead my aim, and this has caused to develop into a better sniper than a camper. I still get >85% headshots and when I am having an off day, I switch to soldier to get some sweet dominations :D