I would call a car with four seats a coupé. "My definitions" are something like: A GT is comfortable, user friendly sportscar with luggage space while a supercar is an extremely fast sportscar where no practical considerations comes in the way of the driving experience.
I'm honestly not sure about the SLR. I feel it's a GT. Maybe because of the shape, which resembles the SL. It is also heavy and it has a rather large boot. On the other hand, it has supercar performance, and Richard said the grip was amazing. The ride is really firm, which doesn't belong in the GT class.
It's somewhere in between the classes...
__________________
|