Did this (Score 4, Informative)

I did this with my AGP GeForce 6800, and the extra piplines didn't work for me. They were damaged. Also you can unlock an extra vertex processor on it, which did work fine for me. I have read that it's about a 50-50 chance that the pipelines will work, as that is one of the reasons they are not sold as ultras. A reason they do work on some cards is that something else was wrong with the card that is also limited on the 6800 model, such as using less memory at slower speeds.