The M3 is faster..
regarding the gearbox, my view, it was ahead of everything else, I can't remember how many Mercedes I have had with 9 speed gearboxes, but its a lot, its really not a problem!
Suspension, the earlier ISFs have harsher suspension that the later ones, mine has Bilstein shocks that apparently make it less harsh, but will in the near future be fitting some BC coilovers as I would still be happy with a slightly firmer ride