As I get older I tend to get less cold tolerant but I have regularly captured images with my Pentax and Minolta SRTs at temperatures that were far below zero, like 30 or 40 below, while snowmobiling in North Dakota. I never had any problem with shutters at that temperature but I did run into problems with the viewfinders frosting over if I tried to lift them to my eyes and use them. I usually scale focused. As for keeping them warm, both the Minolta SRT 101 and the Pentax K1000 rode in a backpack on the outside of my snow suit, not on the inside, so they were usually close to ambient temperature. They were surely cold chunks of metal but both cameras were very snow mitten friendly.

I always chucked the exposed film into the refrigerator as soon as I got back home so they had the opportunity to thaw slowly. And the cameras went in the refrigerator as well otherwise they would start to sweat and had to be left near the furnace vent for a couple days to dry out.

Both of those cameras have focal plane shutters so I don't know how leaf shutters respond to cold. My Super Ikonta seems to do OK but I haven't run across any serious cold here in Nevada to really test it.