get the 6800 GS agp it's unlockable to 16 pipes , 6 vertex units. its basically a 6800 gt.
Actually, that's a curious question. It does seem that some gamers have claimed to have done this, but then again, the same claims have been heard around the PCI-express version; that one uses the NV42 chip, which, like the NV41 used in the PCI-e plain 6800, has only 12/5 pixel/vertex units to start off with. Given the price of producing even sub-par NV40 chips, (and the fact that nVidia has effectively cut production for all NV40 and NV45s) suggests that they really would be using bridged NV42s instead.
However, it's quite possible, for some reason, that they've still got NV40s. However, if so, why aren't they making new 6800GTs? People liked them a lot more than the 6800GS, and even on PCI-express, there's still a bit of a noticable difference in power, and on AGP, it's blatently apparent, as the 6800GS AGP is really nothing more than a plain 6800 with 256MB of 1.0GHZ GDDR3. (much like the X800GTO is the same difference to a plain X800)
I hate to be the one to bring this up, but the x800gto doesn't support sm 3.0. all important feature for new upcoming titles like oblivion.
That's also a curious example to cite, given that the game accomplishes all but one thing under SM 2.0, and that last thing, the tone-mapping component of HDR, (glows are capable of being handled under SM 2.0) is something that many PC gamers have said they won't use anyway, as it's excludes using multi-sample AA on any video card, as the developers of that game have such disabled it. (aside from that, they claim some performance advantages, though some media have suggested that it's a minimal, and nearly negligable, gain)
Most effects that do use SM 3.0 also take up a LOT of graphics processing power, and at that level, it is actually a toss-up whether it would be worthwhile. Most likely starting with the 7600GT, yes, and definitely yes by the time you reach tyhe 7800GT, but at the 6800GS/X800GTO level, you'd likely be disabling most SM 3.0 effects for performance reason anyway.