Reading this thread has made me realize why so many people think aiming is hard in TF2...
Seriously guys, get bigger mouse mats and lower your sensitivities. The mouse mat in that KriMz video is not even that big, it's pretty standard sized for gaming mousepads. As someone who used to play with a really high sensitivity back when I had a crappy mouse and a tiny mousepad, I can say that making the switch is not that hard, and getting used to making large movements with your mouse really does pay off. I use a 13.6 in/360 sensitivity now and I actually still consider it pretty high, especially compared to what some of my friends use. I keep this sensitivity just because I play TF2 more than they do (they mostly play CS), and having different sensitivities for different games messes with muscle memory.
Also, never use anything other than 6/11 windows sensitivity since non-standard sensitivities either skip movements or skip pixels. Adjust your mouse's DPI or in-game sensitivity instead.