I have 40mm Nokkians and they seem a lot better than skinny tires on snow packed trails and roads. Skinny but studded would be great on ice.. but I think the skinniest you can get is 32/35mm.
What amazes me are all the extremely fat-tire bikes that pass me on trails. What's with that? Low pressure and floating over everything.
Below is the guy who is riding to the South Pole.