I think if you're careful, you'll be okay.
I have a buddy with a 2009 M3. He runs the stock-size Michelin PS2 all-seasons, and he does okay. He avoids driving in direct snow/slush if he can though.
NOTE: if you have to tackle any sizable or long hills, all bets are off.
And for heaven's sake make sure your all-seasons have lots of tread.
Always do right. This will gratify some people and astonish the rest.