No knobbies, I'd run 45mm or better street tread, like Pasela TG. If the roads are bad and ice is an issue, I'd have an extra set of wheels set up with studded tires.

The point is, an MTB has a studier frame, you can run wider tires with fenders, the wheels sets will stand up to the abuse, you can run a shorter frame with a higher seatpost and headset to gain some stand over inches for those "holy crap!" dismount moments. Take a look at the MTB with drop bars thread, there are a whole bunch of winter bikes posted there. Many will be as fast or faster than a skinny tire bike on snow covered or wet roads.