GTR is really good, although it's one of those sims where it seems like they really cranked up the "driving on ice" factor to make people believe that it's accurate. My favorite is "Live for Speed", which is a physics-based sim and I think approximates the feeling of driving a car about as well as anything else on the market. There's a demo at...
www.liveforspeed.net/
and then you just pay for a license to unlock it if you like it. I would definitely recommend it and there's a "911-like" rear engined car, though none of the cars in the game, with the exception of the BMW F1 car are officially licensed.