The out of the box performance of the Superclocked card is impressive, easily keeping pace with - and in Just Cause 2 beating - the 1GB GTX 460. The only issue is that card can be pushed even further past what the 768MB card can do at its limit.
With a simple overclock the 1GB card can be pushed to the sort of speeds the GTX 470 can achieve.
DirectX 11 Performance (2560x1600)
DirectX 11 Performance
DirectX 10 Performance