HD 7770 is already a very good GFX, as a alternative there is GTX 650 but HD 7770 will suffice your needs as you have G2020 processor so will not bottleneck, just see that you have min 450 watt PSU that is min requirement for HD 7770.
HD 7770 is already a very good GFX, as a alternative there is GTX 650 but HD 7770 will suffice your needs as you have G2020 processor so will not bottleneck, just see that you have min 450 watt PSU that is min requirement for HD 7770.