Maybe consider getting a Jacks'r'better wearable quilt like the sierra sniveler http://www.jacksrbetter.com/Wearable%20Quilts.htm. That way, when you are tooling around camp, cooking, or making coffee in the a.m. you can wear your quilt serape style and save on having to bring a down coat. The true essence of ultralight backpacking is multi-use IMO. Fiddlehead is giving some good advice as well... you will be at the most risk when not moving.