Yup, the FX-60 would be best, and right below that the 4800X2. Problem is, both are going for so much on eBay that you should buy a new budget AM3 CPU/board/and RAM for the same price
. I would only consider upgrading your CPU if you had a nice high end board and dual GPU setup while simply wanting a little more CPU power to complement your card. Since your board is only meant for single cards, and mid range at best, I wouldn't bother.