there is a vid out there, maybe xboxyde?, of test drive and i thought the frame rate was ok. im sure it will get better from the vid but it didnt seem unplayable. i also like the free driving route they took and from what i saw in the vid even though the game wont match PGR3 in near-photo realism, it still looked damn good considering how huge the game really is.
PGR3 is a must buy for me as its one of my fav. racing series and a great game to showcase what the 360 can do standing on its head.
as for forza i think its more then just a safe bet that it will be coming to the 360 and looking amazing.