Hi OP - Winnipeg winter rider here. Go with mitts when it is cold. Make sure you get ones that are windproof and with a bit of gauntlet to them. Make sure there is air space around your fingers. The coldest I've ridden was -35c at which point the headset didn't want to turn properly. That headset behavior is sort of a temperature limit and a telltale to just not bother riding - kind of like a built-in thermometer. I suppose repacking with low temp grease for the headset would solve that problem but who the hell wants to ride at that low a temp anyways.