So I went ahead and bought the Exped Dreamwalker Duo 400, thinking that STP gave an accurate description of good down to 23 degrees. Turns out that it is actually rated to 45 degrees… I plan to use this when i go out with my wife, so we can share more warmth and be more comfortable.
Like a lot of women, she tends to sleep cold, especially if she is not keeping up her nutrition (iodine, B12, and iron mostly she has to watch). Her bag up till now was a men's 15 degree Sierra Designs dri down bag (Zissou type). The couple of times she has come out with me in winter, she has been a little cold in it at around 30 degrees. For reference, we both have the Big Agnes Insulated Air mats, which are supposedly good down to 15 f.
My plan was to return this bag to REI (it's only been VERY lightly used so far), and give her my mens Sierra Design 30 degree bag and I will carry the Exped D.D. 400. I'm a warm sleeper, and with a down jacket, warm hat and light balaclava, i know i can easily take a 45 degree quilt down to at least 25 or so–especially if i'm sharing some warmth with her as we would both be under the quilt, though she in her bag.
My question is though, how would she fair with being in a men's 30 degree mummy bag, me spooning her, and the 45 degree quilt on top of us both?
Or more apropos, how low do you think she can go. How far can she get down, with the double down, etc. and ad infinitum?
I would like to think that with a down jacket on, some warm pants, that she should be able to be comfortable (as a trend) down to at least 25 with this set up, but that's purely wishful guesstimation. What doth the Clo experts and/or women who generally sleep cold say?

