I am often on remote locations and Expeditions. On a dogsledge Expedition i used a 1dx and a 5dm3. Temperatur was allways below -20C. We were staying in a tent and could only warmup the batterys in our sleepingbags. The 5d did well but the 1Dx did Not operate with autofocus. I never had these problems with my 1Dm3 and1Dm4.
The main problem in extreme cold are the batterys (and your nose) but never the autofocus.
The main problem in extreme cold are the batterys (and your nose) but never the autofocus.