Another thought is to run a decent but speedy tire on the back (like a Schwalbe Marathon Winter or a Nokian 106). Then have two wheels that fit the front of the bike and switch them depending on weather. While I would NEVER recommend running a non-studded tire on the back (I know 3 people who have tried this, then had a big crash because of it and immediately bought a 2nd rear tire), I think it's very different having a faster studded tire in the back and a more grippy one in the front. For one thing, the Peter White site claims that the only reason for side studs is to deal with icy ruts - they don't help with cornering traction anyways. So the front tire plows through the rut and the rear tire still has enough traction to push you forward. So you could have a marathon winter on the front and back for better conditions, then swap just the front wheel to one with a Nokian w240 when you get a blizzard.