Originally Posted by ThomasMcA

If you ride through loose snow, you might want clearance for the snow that accumulates on the tires. Other than that, I would get the biggest size I could get.

I just received a pair of 700x30C Schwalbe Winters for my new Motobecane Turino, so I'm one step ahead of you (and they were delivered in July!) I mostly ride on paved roads that might have black ice, plus the occasional snow storm, so the Winters will work better for me than the Marathon Winters would.