I haven’t used it in the mountains yet, but I bought a slumberjack ronin 0 degree a couple years ago, and have used it in early spring here in Kentucky in the 30 degree range, and had to keep it unzipped. But it’s not exactly light weight at 77 ounces.
Sounds like that’s near the same area I will be headed next year. Going with some family and friends that have been there a few times. We’re going to put in for 1st season, but planning on 2nd season, since we’re applying as a group.