I haven't played QL yet, but it's probably a placebo because you can see more on the sides. If you want to change your sensitivity to match it, try multiplying it by 1.22. Whatever works, really.

Lol.

google widescreen fov calculator

The sensivity is the same but does not feel the same due to the fov change.

so if Im now used to play at wide screen and then go to a lan party with standard 4:3 screens, will it be difficult to adjust or is it the same ?

well, keep the same sensi but use the fov calculator to get the same feeling.
I was at several ET lans, coming from a 4/3 and playing on 16/10s.
The first one I kept my fov (90) and it was kind of alright
The other ones I took the calculated fov (100) and it was almost like at home.
But for extreme fov values, it will give you shit results (eg fov 110 on 4/3 gives smth like over 130, and opposite, 90 on 16/9 will give you a fov under 80 ... kinda unplayable.) I'd advise to take a value inbetween and get used to it :D

e: my point being, as you wont be able to have the exact same feeling, just take what seems ok and concentrate on your game. It has less influence than the mood you're in during the game.

r_customaspect 0 = 4:3
r_customaspect 1 = 16:9
r_customaspect 2 = 16:10
+ correct r_mode from /modelist

and it should feel the same as before