Well thats quite difficult because I've set myself an unusual target for GT4...........
I'm trying to complete it without buying a car.......so as you can guess its a slow process.
Around the 'Ring I've driven various AMG Mercs, M3, Seat Leon Cupra R, Smart Brabus Roadster, Clio, RS4 and a Countach Quattrovalvole.
My only complaint with the 'Ring on GT4 so far is that the track is too accurate in that it is very narrow for a simulator/game.
The lap times in real life are not the same as the game because the gamesstart/finnish line is where the old and new track meet which is a slow section. In real life there is a gantry about 3/4 way down the main straight and thats where you start your watch, and the is another gantry about 10 seconds after the last corner. So in the game you get to take the whole of the main straight flat, which you can't in real life.