i know it has been reported in the past to be running at 30fps on unfinished hardware but this new preview states its running at 60fps. he was playing the build with the developers so maybe there is some truth here.
Wired took the 360 for a test-drive with Gareth Wilson, design manager for Bizarre Creations, which developed the Project Gotham Racing franchise. PGR2 showed off the original Xbox's graphical muscle. PGR3, optimized for Xbox 360, approaches photorealism. Here's what upgrading gets you.
As seen above (and in all the images here), the 360's graphics processor uses 4X anti-aliasing to smooth out the jagged, stair-step edges that plague older platforms. Each frame is scrubbed four times to erase jaggies, and PGR3 still runs at 60 frames per second - twice the rate of TV.