Ok. I've done some testing (2 lap race with each car)
Here are my results in order of test.
BMW M3
Lap 1 - 2'45.921
Lap 2 - 2'42.624
Total - 5'28.545
Notes
Very stable car, quite easy to drive, probably a good enduro car.
Mercedes C63 AMG
Lap 1 - 2'45.027
Lap 2 - 2'42.917
Total - 5'27.944
Notes
Very oversteery, over the course of a 2 hour race the tyres will start to deteriorate rapidly!
Alfa Romeo 8C
Lap 1 - 2'45.847
Lap 2 - 2'41.166
Total - 5'27.013
Notes
Understeer to snap oversteer, not great.. It is controlable but will require some effort.
Aston Martin DB9
Lap 1 - 2'44.837
Lap 2 - 2'39.873
Total - 5'23.710
Notes
Very nice car, very stable and nice to drive, have to watch the front tyres tho.
TVR Tamora
Lap 1 - 2'43.041
Lap 2 - 2'40.048
Total - 5'27.109
Notes
On the edge all the time, going to be easy to make mistakes with this. Felt neutral tho through the corners which is good.
Maserati Gran Turismo
Lap 1 - 2'46.161
Lap 2 - 2'43.299
Total - 5'29.460
Notes
It looks fantastic, sounds the same but drives... ****!
Mercedes SL55
Lap 1 - 2'43.516
Lap 2 - 2'40.877
Total - 5'24.395
Notes
This car supprised me, very understeery so tyres are an issue but it was just so planeted and stable, buig and heavy so had to break very soon.
So in order of the fastest total time.
TVR Tamora
Aston Martin DB9
Mercedes SL55
Alfa Romeo 8C
Mercedes 63 AMG
BMW M3
Maserati Gran Turismo
Please dont take these results as gospel, the SL55 had 2 tries as i span off on the first, i also messed up lap 1 in the 8c so im sure they differ a little.
Best of luck picking a winner