Those results are complete rubbish. The preformance gain from the clock speeds alone is going to be HUGE. Find another review, that one is b0rk3d. You must also take into account that the 512mb 7800gtx uses 1.1ns memory, where as the 256mb 7800gtx uses 1.3-1.4ns memory, so that just proves the results are totally screwed up. Mabey they were using old drivers.
so, umm, err yeah