IF you are concerned at all with REAL winter condition performance, you want/NEED the narrowest tread width you can possibly fit onto your given wheels.
Look at the 'pizza cutters' used for the Swedish round of the WRC, held (if conditions are 'normal' for that time of year) on snow covered frozen lakes, and packed snow fire roads to get an idea.
The only time I've ever heard that a wider tire even could be of benefit is when there is ONLY a 'black ice', or pure ice condition, (given the proper soft low temp compound, and trillions of micro-sipes, tungsten carbide studs, etc.) and I'm not even certain THAT is correct.