I just got a PNY 5800 Pro. So far I've noticed:
It's a little slower at UT2004. 10X7 4X8X 60s-70s instead of 70s-80s I got with 9800 Pro.
Not as noisey as I expected.
Noticeably worse at Far Cry, oh well, didn't buy it for DX9 games.
Just threw it in and changed drivers, no format yet.
BTW-it's as I expected. Without the framecounter on, I wouldn't hae known the difference at UT2004.
Don't buy that hype "ATI AA is superior" BS