Crossfire two 6950 2gb instead of a single 580.
Downgrade psu to a quality 750-850 watt.
IF you are WC then the 800D is perfect, for air cooling in that price range there is the FT02 and the HAFX.
You should probably get some form of cooling...
This is the most help I can give based on the OP. You need to tell us what your uses will be, what resolution your monitor is, and so on.