I too live in Calgary, and have commuted for 7+ winters now.
My less expensive - Gary Fisher Piranha - ATB bike is actually better on really bad days than my more expensive - Norco Fireball - ATB bike. The Altus shifters continue giving me all 21 speeds, while the LX/XTR shifters freeze up leaving me with about 7 of 27. Only complaint is it doesn't have disc brakes...discs (hydros) are definitely better in all conditions (IMHO).
But a couple degrees off the worst days, the Norco shifts fine, and is SSSSOOOO much nicer. The alumimum frame is lighter, the range of gears is better, the brakes are more easily modulated, the suspension fork takes the edges off the icy rut (important to us on the high side of 40), etc.
There are 3 sets of wheels for the Norco - the slicks for spring, fall & really nice winter riding, the mountain wheels for most winter days (weather isn't entirely predictable) and studded front / downhill rear for the really bad days (actually, the studded front is on alot...rubber side down is just so much more fun). Gary Fisher has MEAN Stud on the front/downhill on rear.
Don
Note: I have picked up a suspension fork (my kid upgraded his bike) and if it fits the Piranha, the Gary Fisher will have a front disc and suspension for the coming winter.