I use to have a 9800 Pro. I did the same by returning it and paying $50 more (best buy is customer friendly) for my 6800oc (with warranty) that i have right now.
ATI 9800 Pro = 5721
BFG 6800oc = 8851
A 64.3% increase in 3Dmark03. Not bad for a card that is $50 more than my original. Enough with the generic benchmarks, how about gaming? Farcry, a DX9 game. With my 5900xt/9800 Pro, i had horrible lag in the beginning of the game after it loaded (although it was because of my whole setup though). After i bought the 6800, and install it, there were barely any lag (regardless of my setup and it's salavged parts. Edit: Also, it's Overclocked by BFG, and backed up with warranty. Usually stay around 44c-54c at full load.
^^These are my opinions though, so do not take them for granted, although it might convince you enough to get one.