I don't know what kind of PSU you have, but, for simplicity's sake, you could just throw down for a GTX 960. It's a great 1080p card that's energy efficient, and you won't have to worry about swapping drivers and that other nonsense. It's AMD equivalent is the R9 280, which requires more power, but is generally cheaper.
If you're willing to spend that much money, probably the best bang-for-your-buck right now is the R9 290; you can find some for $250. With an FX-6300, there will be some bottlenecking, though, and it requires a lot more power.