Well I've got the winter marathons, which are studded so its kinda apples to oranges but so far so good.
In the snow, they're not much better than the knobbies I ran last winter, but on the ice or when there is surprise ice underneath they are great. The added confidence is also nice (no more ice surprises)

I do like the reflective sidewalls, and they're reputed to be fairly puncture resistant (really, who wants to repair a flat with a stiff tire like a schwalbe in -10C!)