If you have a decent budget of $1,200 why saddle yourself with a crappy CPU like the FX-4100/4170? If you want to stick with AMD, then I would recommend the Phenom II X4 955/965. With your budget you should be able to afford an Intel Ivy Bridge i5-3570k.
Dude if I were you I'd just buy a Phenom II x4 965 Black edition. They are (supposedly) better than the quad core FX CPUs, and it is the same price. If you are really heart-set on getting a FX I'd just wait until piledriver and see what it's like.
Agree best idea would be Intel i5 at this point. Or if you can wait, a Piledriver FX chip. If you can't wait, and don't want Intel, your best bet is a Trinity A10 APU - though then your FM2 socket might be a dead end.