I hope you do not get your hopes up to much after hearing the PR machine talking about 10x the poly count from Forza2, because they might be right but they are not talking about actual gameplay.
From a post from an Turn10 employee , directly after the E3 presentation, comes the following information.
"Originally Posted by Tofu R:
So...a broad overview:"
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Other things that got cut:
Weather
Night/day
Active aero (again!)
Widebody kits with 12 inch wheels
Some really cool driver animations
Some digital gauge animations
Custom underbodies (with rollover comes undercarriage modeling - unfortunately, all the cars use a generic layouts, so sometimes they are wrong; like the Lamborghinis have the transmission rearward of the engine instead of infront, etc.)
Super high level of detail car models in replays (Currently the super high detailed models are used in the UI homespace/garage, thumbnails, livery editor, and photo mode).
No exposed suspension cars like Ariel Atoms, Lotus 340Rs or Caterhams, even though T10 owns PGR and they had the tech to model working suspensions.
Game still looks mighty good to me no mather the amount of polys used
and a big step up from Forza2 👍
PS: A physics engine runs in Hz, calculations/updates a second, but is not related to the FPS (frames drawn each second on your screen)