Worth getting new mobo for FX or i5?

Hello,

I'm upgrading my PC this Christmas and I need a new CPU for a EVGA GTX 670 because I currently have a Athlon II x4 630. I was looking at the somewhat new Piledriver CPU's and for the most part people are saying that it is better than the previous Bulldozer's and even the Phenom II's. However, after getting the card my budget will be around $300-$400 depending on how much money I get, and either way I will have to get a new Mobo If i want an AMD FX or an Intel i5 CPU.

Bottom line is, should I keep the AM3 Mobo and get a Phenom II processor, get an AM3+ board and an FX, or cough up the cash for the i5 3570k+mobo and not get more RAM and new games?

I am using this computer almost entirely for gaming. The only other things I do is use Firefox, Microsoft office and rarely Photoshop.