Sami
This M6 had a manual transmission. I have driven a few E46 M3's and an E60 M5 with SMG before. The gearshifts are much faster with SMG...as expected but shifting gears manually is just too much fun.
Having said that, the M6 was a HUGE dissapointment. The car feels heavy and the steering is surprisingly dully for an M-car of this caliber. The shifter wasn't the best or the most positive in engagement but I would still take it over the SMG. I had the car up to 128mph and the car was rock solid.
To sum it up, I think the 128i and the 135i with manual transmissions feel a LOT more like M-car's than the M6.