"My advice would be to not ask for advice on a forum, especially this one...."
NOBODY can answer for you.
1. You want to step up to a more professional camera which usually means medium format.
2. You have some very unique circumstances, cold weather, shoot photojournalistic style (sometimes), need a film solution.
3. It's really your call. What matters most is what will let you get the shot and secondly what will give you the experience and results your after.
4. Your going to spend a lot of money and money is important so nobody can really tell you what to do.
I use Contax, have for a long time, will continue to, though under your brief description they are not cameras I would want to use in -50c conditions.
They're great cameras, shoot film and take digital, very sharp and slightly over crisp lenses and can be quite robust.
Flip side is they use a lot of batteries, can be finicky if not cleaned with regularity and are not the lightest cameras for carrying a long time.
A lot of people are going to suggest the Nikon d800 and it seems a good camera, though I'm not the biggest fan of modern cmos sensors. I find them very subject and lighting dependent in color and tone.
I like ccd cameras, just because I think the images are more predictable and look to me to be sharper and cleaner. (just my opinion).
I should add that my Phase backs are 100% bulletproof. Never an issue and I use the heck out of them in all kind of conditions, (except -50c) I won't do -50c heck I hardly will do Moscow in the winter, next to a heated grip truck.
If you want to shoot a ccd I would suggest three cameras I don't use.
The Pentax because it is robust, the lenses are lightweight, and that Kodak 40mpx sensor does fairly high iso well. An extra Pentax film body would weigh little and cost very little. It also uses film inserts that let's you preload with less weight than loaded multiple film backs.
Also I believe the Pentax uses lithium batteries which I would think would be a deal breaker in the weather your shooting in.
Then a tie between the H4d 40 (same sensor as the Pentax) and the Phase 40mpx because the Phase does pixel binning and allow you to go to higher iso.
I wish you the best of luck, hope your trip is profitable and enjoyable.