If you want sweet snow and ice traction while still being able to wheel I would highly recommend buying some 31' s of the BFGoodrich AT/KO's
Sipe them and they will rock!
I have never run better tires on snow and ice that can still go offroad well.
Thornbirds and any other MT suck in the snow and rain even if siped. An AT will be much better. I have found my Goodyear MT/R's have handled quite well though even for an MT. They are pricey though.