Yes its already had a leaked tech demo, and a proper demo without sim mode. And its out in Germany, and most of us racesim nuts have already got it. But as its due out in this country in a few weeks, i thought it was worth posting.
This demo has the Spa Francorchamps circuit - but its the dawn version (as in the game you can do the whole 24 hour race).
The cars are Saleen S7R (GT Class) and Ferrari 360 (NGT Class).
Give it a whirl
http://www.3dgamers.com/games/gtr/downloads/