I'm not sure where exactly the OP is located, but they said about 7500' elevation. I checked the yearly average temps in Laramie just for grins. That's in southern Wyoming at 7165' elevation.
Average overnight lows are below 30F from mid-October to May 1. December, January, February and a few days on either side average below 22F; average daily highs are in the 30s for that same period.
5W-30 synthetic seems like an ideal oil for the car's location and duty cycle.