Depends on the game.
Also your monitor's resolution will affect performance.
If you wish to play a new, gpu intense, game like Battlefield 4 at max settings 1080P, you'll need to buy a highend discrete gpu like a r9 270x/80 or a gtx 760/770. Your CPU may bottleneck. To avoid this you will need to overclock your CPU, you'll need a after stock heatsink like a Raijintek Aidos or better. OVERCLOKCING VOIDS YOUR CPU's WARRANTY.
If you want to play older games like Civ V or Skyrim at 900P, you can crossfire your GPU with a HD 6670, YOU CAN NOT CROSSFIRE WITH ANY BETTER GPU SAFELY.
I am upgrading my A8-5600k by adding a R9 270 (Maybe better if the prices drop.) and overclocking my CPU to 4Ghz+ with the Raijintek Aidos.