OM,

I'm glad you mentioned it being colder at lower altitude. That has been my experience in Colorado but I didn't want to say anything. The coldest sleeping seems to be around 9,000 feet here.

SNS,

Since you are comfortable in Colorado with a WM 40 degree bag, I would think you could do well with a WM 20 degree bag, but don't take my advice. There are many WM dealers in Colorado. You can find phone numbers on the WM site. I suggest giving them a call.

The owner of Mountain Chalet in Colorado Springs has done lots of backpacking and, if he has time, is willing to share info.
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