Best 939 processor

I have a msi amethyst-m what is the best processor for this board?

If you can't find the FX-60, which you probably can't, then the next best thing was the Opteron 185. The only difference between the two was that the FX-60 had an unlocked multiplier.

I think you are better off doing a full upgrade. The only place you will find FX-60s now is ebay. I got an FX-60 right as they were EOL'ed (for around $200) and it was and still is great, but even with a 4850 the rig is really showing its age (DDR1 is a bit limiting now). You would probably be better off starting over, but no harm in checking ebay I suppose.