My inclination here is to go with the 750k. For gaming, nearly every dollar possible should go towards GPU if possible. However, do you have a MC nearby? I've bought quite a few FX6300 + Mobos, and with the combo savings it usually totals something like $120 for the mobo+CPU.
Okay, just went and double checked, look at this :
I've got roughly that same setup (FX6350 + 990 Mobo + 7870) in my HTPC, and it happily churns through anything I throw at it @ 1080p. Even with the 7870, I'm GPU limited.
The Intel Quads and above ARE better, but who can argue with a $120 Hex + Mobo? I prefer the 6er to the i3, Windows just feels better.