Just something came into my mind.
Turn 10 said the Forza 3 cars polygon count is 10 times Forza 2 for each car.
Rumored that Forza 2 had around 100,000 polygon per car.
Simple math says Forza 3 cars will have average around 1 million polygons per car while GT5P only average 200,000 per car.
Now 8 cars x 1 million + tracks and stuff, it easily exceeds 10 millions polygons per race.
If GT5P's 70 cars @ 200k polygons each and the 5 tracks + physics/sound data needed 5GB of space, how is it possible to fit 400 cars at 1 million polygons per car (kind of equal to 2000 GT5P cars) and 100 tracks (let say around 35 unique tracks) + physics/sound data in 1 single DVD?
That's with my assumption that they don't split up the cars and tracks into 2 DVDs to avoid disc-swapping in the middle of car picking.
I wonder how would they manage to keep the core game/modes in 1 DVD with all the cars and tracks.