This is a FM2 real vs game comparison at the Nurburgring camping area, about 2/3 of the way through. I'm not all that impressed. Remember GT4's? Some were so good that people failed the real vs game quiz.
There are layout and elevation issues here. Curbing and barriers/fencing in the wrong location, the environment is off in many ways.
http://www.forzacentral.com/gallery/files/4/8/sim-forza-0387.jpg
Let's see how many differences you can find in this comparison image, too, including track width and elevation (which affects car handling), again. That hump before the sharper hill is pretty noticable.
http://www.forzacentral.com/gallery/files/4/8/sim-forza-0388.jpg
Cheers,
MasterGT