the 7770 would probably give more fps overall. if you don't have the apu yet, get an athlon x4 760k and use the money saved to get a better graphics card. otherwise, save up for a 7850 or R9 270 and just use the integrated graphics for now.
While you'll see a bit of a performance increase with dual graphics, the scaling is not where it should be, frame pacing is an issue so you'll get a lot of micro stutter (where the game displays 2 frames back to back then a long gap before the next 2 frames). It would be much better to save your money and get a better gpu.