elsewhere on the forum i saw that someone did successfully run a 8800GT on a sub PCI 2.0 bus, they did also see performance gains of about 3000 points on 3dm06 i believe. That is to be expected with almost any dx10 card as 3dm06 doesn't have a dx10 component that i am aware of.
I think that if you were to later transfer that card to a PCI 2.0 board that you would see further gains even if you somehow managed to keep the same RAM and CPU (if someone had the resources to -*test*-('") a PCI 2.0 bus versus a PCI 1* that would be cool) They talk about the diefference
here a little bit, i didn't read the whole thing. It appears that PCI 2.0 will have a greater effect on cards that are in SLI or with some nefarious applications. I didn't see any factual evidence as i skimmed through that thread.