Just wanted to chime in with some relevant information for anyone considering this card. I purchased the BFG 6800GS OC AGP from mwave.com last week, and so far I have been thoroughly pleased with it.
One minor issue, the current latest WHQL driver available on NVIDIA's website (81.98) does not support this card, despite NVIDIA's website listing the 6800GS as supported by this ForceWare version. As a result, BFG ships this card with the non-WHQL 82.12 ForceWare revision. So far, I have had no problems with this beta driver, but I just wanted to mention this as a heads-up since I was initially frustrated by trying to install the WHQL driver with no success.
On the issue of unlocking the extra pipelines to turn the card from a 12x5 pixel/vertex pipeline configuration to 16x6, I was able to unlock mine with ease using Rivatuner. Rivatuner griped that it has not been tested to work with the installed drivers, but it does not appear to have any difficulty accessing and modifying my card's settings.
The only problem (if you can call it that) that remains is that, since unlocking the pipes in Rivatuner, neither the Coolbits settings in the NVIDIA control panel nor Rivatuner will allow overclocking of the card. When you click to test the new clock settings, it instantaneously comes back and says the test failed, and will not let you set the higher clock speed. A minor issue though, as my 3DMark05 score and performance in several games was noticeably better after unlocking the pipes.
A great buy, if you have an aging AGP8x card and don't want to upgrade your whole platform to support PCIe cards, it's a great value.