it's for that 16bit dithering issue.
by the way, I would use a Voodoo5 PCI rather than a Voodoo3. or given that money is no concern you can have a Voodoo5 6000 on an AGP to PCI converter
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Voodoo5 gives the better 16bit@22bit. but if you're crazy on IQ, its texturing filtering (bilinear only) is only good with 4x AA and LOD -1.5. Which is a heavy setting due to the AA, but then the textures are really great.
The PPU thing looks more crazy to me. 2008 IQ, you should cancel that order on the Asus PPU. a piece of hardware that will run one or two tech demos and will be too slow for any future game that can use it, it's next to useless.