There will most likely be some key features found in Rampage that won't be able to be performed by the NV20 chip, such as QuadTexture rendering in a single pass. I think some of the features found in Rampage won't be available until DX9 comes out, but that's probably because they couldn't get it into DX8. Hehe, go figure. Either way, you can expect the big features found in todays hardware, other than a Voodoo5 of course, that will be found on Rampage. Propoganda game sake of course.
Speed is something of the other matter though.
There are a lot of features 3dfx is keeping very tight lipped about that none of here know about. I can confirm that it is a true story, even if the facts are a little blurred. I mean the Geforce actually has some meaning to do with it. In fact, it's just an extension to the accumulation buffer. The T-Buffer and 3dfx's RGSS FSAA doesn't follow API specifications, it bypasses it.