Man, I've tried to share my info with you around here but you just keep denying me...
6800u stock - 5300 3dmark05
7900gs - idk..maybe mid 5000's to low 6000's
6800u oc - 6800 MAX ever 3dmark05
7900gs oc - chills at 9000 3dmark05 and some hit 10000
Edit: yes the stock differences between the ultra and 7900gs aren't too big but the kicker is that the ultra is already on crack while the 7900gs is cold turkey