@HoiDaniel, no I haven't overclocked anything...
@FatPenguin, those 2 video prove that it should be enough for my needs
@Kyuubixchidori, I checked and usage of GPU is 98-99%, CPU is around 50%
@Morgan MLGman, my drivers are up to date, and I checked RAM for defects, windows tool says it's O.K.
@Emanuel_M, 720p on 20" Monitor looks ugly.
And as always thanks for your help, I will try with overclocking CPU and Vice Versa. PC is 2 weeks old, I bought it new for 300$.