The Athlon x4 750k and 760k are really good for the price. Everybody is harping on about and drooling over the new unlocked pentium cpu but I wouldn't get a dual core cpu for gaming in 2014...it wouldn't fare well in modern stuff like bf4 multiplayer, and it's not like the AMD would be unplayable in older titles as they would obviously be less demanding.
My bro has an a10 5800k with a gtx 660ti and he has been able to play any game he wanted on 1080p ultra perfectly fine. Not constant 60fps in every game like Metro Last Light, but without the little FRAPS FPS counter in the corner I honestly couldn't tell when it dipped from 60+ fps to 40 or 30s. On BF4 multiplayer on some maps his PC matched mine, at the most I beat his by 5fps. And his cpu is essentially the cheap 75dollar Athlon x4 750k
In short, it would be a great improvement over what you currently have. If you could spend a little more for the fx6300 and a good motherboard that would be better, but the 750k paired with a decent motherboard at 4ghz (or 4.2ghz as my bros a10 5800k goes to) would be pretty good. For a long time it regularly got the best CPU for the money on a budget for 1080p
just depends how much you want to spend and what you'd like. Sometimes with how much an fx6300 and good motherboard costs as well as the heatsink, you could get an intel i5 and h81 motherboard combo for the same price, if not cheaper.
AMD isn't as bad as the elitists online portray them out to be. I'm really thinking about building an fx6300 secondary rig myself, or an athlon 750k and pair it with the gtx 750ti
The gtx 660 is a little better than the gtx 750ti, you should be fine playing stuff even on ultra on 1080p with stuff like MSAA turned off (even I do that on my pc and I can't tell a difference) or at the very worst on high settings.