Agreed (though it does depend on location - summer tire is probably ok to winter in Florida or southern California.Agree with the inputs from all. I found that in winter, I don't want to push the cornering adhesion much at all, even with the all seasons. It will step out on you with little warning and give your heart a little shot of adrenalin. I would not be personally comfortable driving a summer only tire in winter temps. I'm enjoying my life too much at present to dance with the devil!
I am in upstate NY and will be switching on my snows this weekend (don't trust all seasons in the winter on a Mustang of any variety - way to slick in snow and ice). Mornings are projected to dip into the low 30's next week - a bit too cold for the MPSS I am currently running.