As disappointing as the FX-6100 was when it was used in a SBM a few cycles ago, I agree with Tiny Voices that a GPU upgrade only won't give you the increases you want. Hopefully you can fit a FX-6300 (or FX-6350) and a GTX760 or HD7870 into your budget. What is the brand and model (not just wattage) of your PSU? A unit strong enough for the HD6850 may not be quite enough for a major upgrade, so checking is a good idea.