I ran a similar question in Commuter forum, but seem to have read a comment somewhere by someone inhere who said they thought a smaller bike gave them more control in winter conditions.
I've been trolling for a better frame for my winter set up (26" tires with a Shimano internal 3-speed in back). Currently its an 80's Canadian made Peugeot US Express (with the ashtabula crank upgraded to a typical alloy crank with some sorta conversion dealio). It works, it's a bit of a beast. I found a cool '84 Trek 890 (very early Trek All terrain bike frame, canti studs, etc). I could pretty easily swap the wheels and bits fromt he Peugeot to the Trek... BUT the trek is around 3CM smaller in frame size. The Wheel base on the trek is about 2" shorter.
I know I can get a tall seat post and some long stem in front.. and my bars are some old school albatross like deals. And I realize one can't tell how it will be until it's all changed, but for Winter bike commuting, is key bike fit not as key? I'm juiced to put the Trek into use, just not sure if the size change is too big