Riding in winter

...but nothing beat huge slick tyres (47c) on snow though...
For snow, you want some sort of knobbles for extra grip. Pure slicks will compact it down and give you nothing rather than biting in and pulling. For sheet ice then slicks are maybe better - the more rubber contact area you can get the more chance of not going sideways.

PS: I've just worked out what these gear inch things are all about. It seems I'm running 56GI (26:12 on 26" wheels). Do you guys on 70+GI just never climb steep hills or am I really that bad? I thought I was doing well getting up steep stuff without gears too!