I used to use an Olympus OM-1 when I worked up north.... I liked it because the only thing that ran off batteries was the meter, and when the battery froze you could guess exposure and it still worked... and the temperatures...-65C, thats about -85F.
Shooting with a 60D in milder conditions (-25C), you quickly find that the lcd display screens stop working fairly soon. I kept the camera wrapped in a fleece blanket to keep it from cooling off to fast.... snap a few shots, then back into the insulation to slow down the heat loss... and once the lcd starts to freeze, I just gave up.
I had thought about making a foam "jacket" for the camera to slow down the heat loss, but never got around to it... but whatever you do, please don't put the camera under your coat to keep it warm because that is a very moist environment and will mean the end of the days shooting and lots of time spent afterwards drying things out.
I carry a hiking drybag with me to put the camera in before coming inside... squeeze out as much air as possible before coming in, let it warm up for an hour or so, then open it up to adjust to the room termperatures.... this gets rid of most of the condensation issues.
hope this helps...