I never had any trouble with losing calves in the Winter, but I always had them on the ground before Thanksgiving. I have several loafing sheds for protection from the North wind and from precipitation. They are arranged with no West wall so they can get as much Sunlight as possible to kill bacteria. I worked pretty hard at keeping the sheds and pens cleaned out and sanitary as possible.
Everyone has their own way of making things work I guess. I got the Fall calving habit from my Grand Dad who was further South in the Hill country with a little milder Winters. I also got the sanitation obsession from him. He always seemed to be raising a few calves on a nurse cow in a shed with Sunlight exposure. His philosophy was that it was all about sanitation and preventing bacterial growth.
All that said, Spring calving is probably the safe play though, and you're right about the loss of a calf or two. The margin is so thin that it's hard to make it up.