I think even the C2's do pretty well in snow due to the rear weight bias. But I've never had mine in snow or ice so cannot say first hand.

 

They do and always have if they have the correct tires and a knowledgeable driver. When I lived in the Northwest and a 911 was my only car, we went skiing every weekend from White Pass to Mt. Baker to Whistler in the 911, and often did better than our friends in their other cars. No C4s back then.