I am unsure if it works on PCI express version, but it might.
PCI express supplies a bit higher power levels to the card than AGP, so it may do even better overclocking wise since there is no way to add a Molex power connector like the Ultras use.
You might be able to find something specific about this if you feel like doing a bit of digging, I don't have time at the moment.
http://forums.guru3d.com/ has an extensive section for NVDIA cards
Let me know if you find anything definative, I am curious too