I'd have to put a separation between a GT car and a Supercar. Grand Tourers, are stylish, fast responsive and expensive, think SLR, Vanquish, Murcielago. They are however heavy, and are filled with electric nonsense and stupid paddle gearboxes (some of them).
A supercar is similar, in that it is stylish fast, responsive and expensive. But it must weigh as little as possible and leave all of the control to the driver. For a car to be Super, it absolutely must scare me every time I drive it with monstrous power, huge speed and the constant threat of me losing contol and flying into a ditch.
I drove a TVR Griffith B340 once, I was white and shaking afterwards after having it all over the road. BRILLIANT.
GT cars hold your hand as you drive (to an extent) a supercar will try to bite it off. That isn't to say a GT car is soft, I'm sure I could crash a Vanqush if given the chance, but I bet I'd crash a Sagaris quicker.
Kurtis.