When you're winter biking, the main motivation for speed is not the cold weather. It's keeping ahead of the snow plow! It's amazing how a large plow can sneak up behind you. They don't go very fast, maybe 25 km per hour, but that's usually a bit faster than you go, even with all your winter layers on and good studded tires.
As soon as you detect a plow behind you, the best advice is to carefully signal a left turn and cross the road to the left to let the plow go by. You can't just pull over to the right because he'll completely cover you as he goes by!