Playing what games. If you are playing flash player games or kiddie games like the Sims than it's ok but if you want to play games like BF3, Skyrim, COD, and Crysis you are going to need a better processor and better video card.
Not really. It is a 5XXX series it is now two almost three generations old and games are only becoming more demanding. I don't know what benchmarks you saw but I don't think it is going to play BF3, Skyrim, AC and stuff like that at max settings with AA on at 1920X1080 or greater resolutions.
As for which one of those to get it depends. If you are planning on using a dedicated graphics card there really is no point in getting the APU. The best feature of the APU is it's integrated graphics if you aren't going to use it than all you are really left with is a dedicated graphics card with a weak CPU core. I would go with the I3.