theres no problem with that tranny. i had the first version on an auti tt. the tranny works very quickly/sharply. its my opinion that all audi/bmw.... should be using this tranny. the auto mode make the bmw step shiftly feel like a new manual driver.
the only issue i would have on the m3 is what the ride would be like. the 650 is the best riding car i have evry had, and that number is too large. if the m3 rides like its 3 series cousin, its too hard for me. i drive coast to coast each year and the 6 series is the only car i have driven that after 10hrs of driving that does give me a jittery feeling.