Thanks for the replies !
As far as I know everything I'm working on is using OpenGL so if I choose the 5770 won't be a problem loosing the CUDA
The thing is that I am not choosing which one to buy. I got now the GT440, but I can exchange it for free for the brad new 5770 as the guy who owns it do not need it and will keep the GT 440 just for spare...
So I'll take the 5770 then.