I work on the North Slope of Alaska, more than one hundred miles north of the Arctic Circle, and until March when I upgraded to a 5D3 used a Rebel XT year round up here. I shot outside many a time from -50 F to -20 F, just shoot brief periods outside and then warm up; I also shoot from my truck keep the camera warm. Batteries go quickly in the cold, that's the real problem.
Don't forget humidity and getting the camera at the outside/inside temperature when it's been in the opposite. Especially if it's been inside and it was just outside which it will get moisture on it, and then take it back outside before it completely acclimatizes. I imagine the moisture will freeze, and start taking it's toll on the physical connections and electronics.