I would also like to know as it is easily my most anticipated game, I logged well over 100 hours on PGR2. Maybe stop by their website and ask in the forums, they read their forums and answer questions all the time.
But Bungie are pretty skilled devs... since they will get to work with the GPU for about a year before hand and already have Havok on Halo2 I think they can do some pretty neat stuff. But there is only 2 years between games, that does not seem like long for a Killer AAA titles :?
I wonder if some of the neater R500 features like higher ordered surfaces and the like will get used. It would be nice for 2006 games to begin exploiting the features that we are craving!