I just got a pair of these a couple of weeks ago. Did great in 40 degree temp. I wear 44.5 shoes which I consider to be pretty average foot size but I followed other's recommendations and got size bigger. I got XL and that was pretty darn tight. If I would've got Large I seriously doubt I could've gotten them on. So definitely up size.
One stupid thing that EVERYBODY does wrong.. not sure why the zipper is on the outside.. it really should be on the inside. Then when I'm putting them on I can put my right foot on left leg to zip up and vice versa. Being on the outside makes for an unusual twisting... but I'll live.