OC Workbench has been playing with a 7800GTX without the power connector hooked up.
One of the features of the 7800GTX is that it can throttle down its GPU performance if power is not strong enough.
Over 6k lost in 3DMark03 and 2k lost in 3DMark05. If you're getting one of these graphics cards, make sure you can power it!

[OC Workbench]