Before getting an AOpen 6800GT I had a a GF Ti4400. Now, playing UT2004 with almost everything off in 800x600 I could pull 90fps average online with the Ti4400. In exactly the same system with same drivers and settings, the 6800GT is in fact slower! Also, in the idle time between maps the Ti4400 shows 700fps whilst the GT shows 500fps. I should add that that is with the GT oc to 418/1.1.
The GT will allow eyecandy, eg 1280x1024 and most on, and still pull 80fps average whereas the Ti4400 is brought to its knees.
So these 6800s do not seem 'faster' than such previous cards, they simply seem to do more in the same time - 4 pipes versus 16 pipes seems to underline this. This is likely why many find Doom3 playable with a lowly card and eyecandy turned off.