Biathlon, thank for the note about EE quilts. That's not a bad price, and I like the synthetic one.
As usual, we have talked all over the map of temps and situations. One bag isn�t likely to do it all well. FWIW basis for my comments: I avoid deep cold as much as I can predict, go light and have bailed out early when the weather turned on me. But I have enough gear to confidently make it.
Every scrap of clothing and gear can help get you through a colder night than you anticipated.
Thinking back, I have slept at least 9 nights in a sleeping bag in -40 or colder without heated shelter. One in the open under stars, a few in a partly covered pick-up bed, a couple on a vehicle seat. In all of those I slept warm and comfortably, though one was marginal. Have slept considerably more camping nights between 0 to -30.
Nowadays if there is a horse or vehicle to carry it I take a second sleeping bag to put over the first if it gets really cold.
