Well, an SMG is an electronically operated(clutch) MANUAL gearbox. it is NOT an automatic box. Having had an E46 M3 6 speed manual an testdriven a E36 and E46 M3 wth SMG 1 en SMG 2 and the M3 CSL, I must say, when gotten used to it irl it wouldn't get any better than SMG, so fast(downshifting e.g.) without shiftlock to the rearwheels, just excellent.
But to play(drift) with a car, I 'd prefer manual 6 speed. And the price for SMG was rather high...
I forgot Ferrari has the 'SMG' system too as an option(or you choose manual) F430, best sportscar at the moment by far. IMHO