Stu, At -40 there's not much difference, and I could make a comment about "nuts" but this is a family friendly forum
Actually at -41C it's -41.8F
I can't offer much more than the great advice above, but I thought I'd show you my winter camera. Doesn't have any issues with the cold at all. Batteries stay nice and warm and there's no condensation trouble either.
With acknowledgments to :
Sewn by Blythe: Pentax Camera