I think SMG/SMG2 can shift up quicker than most drivers. I believe both have launch control too. In the grand scheme of things, they are just manual boxes with hydraulics which change the gears and move the clutch.
SMG (or often called SSG) is the version found in the 330. You here stories about the boxes being unreliable, but not sure how true this is particularly with the later boxes found in the 330. The box started life in the e36 M3 Evo IIRC.
I've passengered in a car with SSG (Z4) which seemed nice - I didn't find the gear changes jerky, but it some might. The auto mode isn't as good as an autobox - but manual mode with the paddles is great. Only car I've ever driven with and SMG2 box was an M3 CS. I liked it, but said I'd never pay a premium for one over an M3 with a manual box. Since exploring track days my opinion on this might be leaning a little - as paddles would be a big bonus.