I do believe sedan and coupe are almost identical when it comes to performance. Sedan are only about 20lbs heavier, but it does have shorter overhang. So i dont think M3 as a sedan would be far from what a coupe would be, so were not really loosing here.
I for one would not buy a coupe. 1being I have 3 kids and a wife. The other theres really none out there that in the sedan category that can compete with it. But as far as coupe, theres plenty of competition, and hate to say it some are far better car than a m3.
That said I dont care if they call it 320sport as long it make me tingly inside when I drive it ill buy it.