I'm guessing the coupe @ 480hp with 3500# of weight. Sedan @ 460hp and same weight.
0-60: 4 seconds and 1/4 mile: 12.0 with sedan two tenth of a sec slower than the coupe in both category.
I'm guessing by the time the M3/M4's out. BMW will tweak the engine for the M5 a bit and make it 600hp.