Advantages!!
Well the BIG advantage is that there isn't a big advantage!
Oh yes! bragging rights, thats a good one and on a slightly more serious note, a very small advantage when run at the highest possible resolutions with large displays but only detectable in a benchmark.
By the time the 256mb will make a differance you'll be wanting another new card.
Much, much more important is the graphics chipset and memory speed, better to get a 128 card with a more powerful GPU than slower graphics chip supported by a massive 256 chunk of memory.
Example of two similarly priced cards:
256mb DDR ATI Radeon 9600XT and
128mb DDR Nvidia Geforce 4 FX 5900XT
The 128mb card, by vertue of it's more powerful graphics processor, performs as much as 50% faster in benchmarks tests when compared to the 256mb card.
Martin
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