I have had fun with other various car match ups. Some require ballast added to one car to make the racing closer, but on average most are stock.. 1 cars strength is the other cars weakness and vice versa.
This is the RUF yellowbird vs the mercedes SLS. I ballast did have to be added to the RUF as it had a bit more power and top speed.
Another mix is the Lotus Exige S and the BMW 1M @ spa.. very close. (looks to be the standard 1M)
To add to the mix of the M3 vs cobra you can add the Lotus Evora S S2 to have 3 makes..I tested both road cars against the cobra and the evora seemed even closer to the cobra for speed.
There was another car we mixed with the Mazda MX-5 cup.. I think it was one of the abarths..