I'd say the only way you are going to get a good amount of comfort under 4 seconds AND have AWD... is to spend $100-130K:
Audi RS7 (or even the S7)
Jag XJR (even that is only 4.4, but a BEAUTY)
Sure there are faster cars for half the price, but like your M4, or an S3, or C63... They are go-karts in comparison.
I think that is what I like about my Q50, it's a nice combo of comfort and performance. It may not be quicker than even a 340i, but it's nice knowing that I'm sitting in a smooth, quiet, roomy, sleek, easy to maintain, honey magnet, "whoa dude, sick ride", kind of car...
I'm still pretty young, but even I appreciate comfort as much as performance. Hence, the reason I ignored half my friends saying "dude, get the WRX, or Pony GT..."
said, the Q50RS has got some potential, and I think you are getting a reasonable amount of comfort with it. Wait for a tune to come out, some sticky tires in the summer, and you'll be closer to that 4 second mark.