I have the MPSS (not the newer 4S), and we did a very aggressive three twisted sisters drive on the coldest day of last winter (20 degrees in Kerrville), and they were fine. Actually they did really well. Drove them all winter in Austin with no drama whatsoever.
Now, as with any summer tire, I'd avoid snow/ice, but for just dry cold temps and/or some rain, they're a perfectly safe choice.