You can use the GT-One ROAD CAR.
The Lotus Esprit GT350, TVR Speed 12, Ruf CTR, Ruf GT2, Viper, Corvette (either one) will all win EASILY with T2 tires.
If you want a challenge, it can be done with the TommyKaira ZZ-S, The Lotus Elise, I believe that the Lotus Exige(Motorsport Elise) may be eligible if you don't buy any mods for it.
The key is your pit strategy. If you can run a 8-10 lap pit schedule you will win by a good margin. Less than a full lap, but a good margin. That is until the last 5 races.