The 'shifting smoothness' of SMG needs to be explained. It refers only to the 'auto-shifting' mode. In this mode, the gearbox attempts to simulate an automatic transmission. It does so fairly horribly!
That said, NOBODY (save a few doctor's wives who bought SMG because they couldn't drive a traditional manual gearbox car .....) uses the auto mode in an SMG M3!! It's a ridiculous feature. SMG is a performance upgrade, not a comfort option.
I drive in S6 (Sequential 6) with the paddle shifters and stability control switched off and Sport mode engaged 95% of the time. Does it shift smoothly in this mode? No - it shifts instantly and VIOLENTLY, breaking the tires loose easily in 2nd and 3rd gears. Is it as fun as using a clutch pedal? It's not even a contest. I would not ever buy a car with a clutch pedal again if an SMG/DSG type gearbox were available. There's a reason why all F1 cars run sequential manual gearboxes .... and it's not because they're slow-shifting.
I used my '04 M3 as a daily driver for about 1 year. It's a high-strung car but it worked just fine for that. The M3 is every bit as fun to drive as a Porsche (and faster than a normal 996/997), but it does so in a stealth/sleeper manner. Most people don't know what it is and don't give the car a second glance.