A thicker profile and smaller wheels would provide better traction, but I think an M3 with 17" wheels would just look gay (even if they are snow tires) and you'll take a big performance hit during the winter. I think you should purchase a set of Replica M3 18" wheels and purchase a set of Dunlop WinterSport M3's or Blizzak LM-22's and use that setup during the winter. It should be fairly cheap if you purchase the snow tires now and go with replica wheels (such as from
http://www.aaarims.com/).
My reasoning for 18" wheels is that on most days of the winter it's not snowing (at least here in NJ/NYC that's the case) and just because you're gonna be riding on snow tires during the winter shouldn't mean you have to take such a big performance hit.