Also keep in mind that 256 megabytes on a video card is almost completely useless. For cheaper cards 64 megs is just fine, and 128 megs is a luxury but justifiable.
You won't notice any performance difference with memory. You might see slightly higher rez textures in future games that support 128 megs of textures, but other than that, no speed difference at all.
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Radeon 9500 (modded to PRO w/8 pixel pipelines)
AMD AthlonXP 2000+
3dMark03: 3529