Extensive Doom III benchmarking has proven that even at higher settings the extra 128mb of memory does not help the 9800 pro any . Does a 2% performance increase justify 50USD extra? Not even for flashing to the 9800XT , as the 128mb 9800XT bios is not to hard to find.
On the other hand , The 6800 256mb has up to 20% of a lead on its 128mb sibling , this can be attributed to a core that was MEANT to use ALL 256mb of that ram, rather than one unwillingly strapped on a board with extra ram as a marketing ploy .
http://www.firingsquad.com/hardware/doom3_...h10244aa8af.gifhttp://www.firingsquad.com/hardware/doom3_.../d3u16004aa.giffor a game that was 'Meant' to use 512mb of ram, 128 and 256 hold up just fine . We can also see that the BETA ati drivers help boost DIII performance a bit and ATI promises 'incremental' increases in OGL performance from now on .
point : for PRE X-800/6800 cards , get the 128mb version , it is better [ and cheaper ] to get the 128mb version of the card. And in some cases.... the 128mb cards are FASTER [ by that same 2%]