I have been doing high-volume courses in arctic conditions since 2007, with mixed assortments of rifle types in the courses. When I say "arctic", I don't mean snow on the ground in CONUS, but actually above 60 degrees north latitude in the dead of winter. Most courses in these conditions have been at least -27 C.
What surprised me was how well a properly-built M4 will actually run, even suppressed. I still use Slip2000 in those conditions, without issues.
I did break the first generation of Magpul MIAD grip, as it used a conical screw that split the grip in half. The retaining tabs for the back strap also cracked, as did the grip core tabs. It made me appreciate a standard or similarly constructed pistol grip, that doesn't have small portions to it that will easily fracture in extreme cold.
I also see a lot of FTFire's with AK's in these conditions, but they do that in the summer too, so the reliability myth of the AK hasn't held true in my own experiences dating back to 1998.
For dusty environments, I recommend a thick lubricant that has volume to it, with staying power. Basically the opposite of CLP. The thick volume lube will keep dust from being able to get into articulating parts that have lubrication between them. Eventually, fine dust will work its way everywhere, especially when riding in vehicles, but the thicker lubricants keep a gun running longer.
Be habitual about keeping the ejection port door closed, and the BCG coated with thick lube. Even motor oil works well in this regard.