Haha yes thats right, I understand with 300W is a bit hyperbole to mention "punch" but nevertheless i am expecting something like 460. Even lower a bit is okay. 7770 is out of my budget at the moment so i might lean toward 6850.
I just calculated above spec with PSU calculator and with 6850 min PSU recommended 238w and max load is 288w. Assuming 80Plus PSU, seems should be all right.
If i am going down G620 path for CPU, what is cheap reliable mobo to match with (approx. equivalent to planned mobo)?
Thanks for all the expert replies!