Royal Purple makes good stuff…. Very expensive compared to other synthetics, like Mobil 1. 1 quart of RP gear lube is $100!!.... 1 quart of Mobil 1 is $13.00
If I were living in an extremely cold climate, I’d be running all synthetics… gear oil, auto transmission, motor oil, wheel bearing and driveline lube.
The only real advantage with synthetics is they flow better at very lower ambient temperatures. So getting a little better lubrication during the most critical time needed…. Cold starts would be an advantage over conventional lubricants in terms of potential wear factors.
Now.. how much difference will it make?..... Your drive train probably will not be able to let you know. Engine , drive train, differential, or U-joint failure is rare where failure can be attributed to a specific lubricant if maintenance is performed by the factory recommendations, or according to application.
If I ran synthetics to replace conventional dino lubricant, I would buy Mobil 1 products.
Using Royal Purple may make you feel better psychologically, but it will definitely put a little Purple ding in your checking account.