I found some info on the web on this and decided to try it on my 06' M3 convertible. There are actually two modes; one mode pulses the clutch for less tire spin and the other mode dumps the clutch for a smoky burnout. I think that if you floor it to the kickdown switch, you get the burnout mode although it does start the revs at somewhere around 1800 rpm.
I don't think that it's going to be as fast off the line as a 6 speed but the SMG mode 6 shift speed is really, really fast so the 2-3 shifts are actually faster than you can do with a stick.
Follow this link to a manual on the SMG
http://www.m3smg.com/files/smgmanual.pdf
also good information here:
E46 M3 SMGII Special Functions
This is very hard on the clutch so I wouldn't make a habit of it...