After my Atom snaffu, I rethought things and ordered a Summerlite. Push came to shove, and I took your advice to heart, Don. The full-length zipper and baffles, WM's reputation, and a bad taste in my mouth after having gotten a vapor-barrier Campmor Marmot Ion added some extra shoving power, as well.
Temps are going to be around to above freezing here tonight, so perhaps I'll give it a try. Just from a first look, it is a beautiful bag. Impeccable stitching and craftsmanship, great zipper, the fabric feels great, the down lofts up higher than 2" between the baffles, the hood is comfy. I'll hold off any real judgments until I get some use out of it, but I don't think I'm going to be disappointed.
Thanks, all, for the advice!