I haven't really given this to much thought but basically I see it as....

If the car is a "faster" version of a slower car then it's not a super-car. There are exceptions though, maybe if the "slower car" is already ridiculously fast. A GT3 is a super C2 but not really a super-car. However, an F430 is not but a Scuderia is. A DB9 isn't, but a DBS is? What's a GT3 RS? I think it' still a Carrera but then again I think a DBS is a super car..
Price plays a huge role, but then again so do raw numbers. I think the exclusive factors outweighs both of them