Technically speaking fast = top speed/velocity, quick = acceleration. Musclecars are known for straightline acceleration (with short duration high speed capability). I'm not referring to cars that can chirp the tires, but to ones that can envelope the car in blue burned-rubber, pavement-shredding smoke...or lift the front end off the pavement as they launch.

Sports cars have traditionally been European-based designs. Something like an MG midget. They are indeed fun to drive and are quite nimble, but let's not confuse them with "fast" cars.

To be fair to your definition, the American version of sports cars typically has a V6 in it (as opposed to European versions which employee a few squirrels in a cage). As such, they are much quicker that Euro-cars but certainly not fast (in a long duration high speed touring application).

Let's just agree that whatever our definitions, they're all super fun to drive.