Ive often wondered just how much warmth a 50 degree overbag would add to a 15 degree bag in real life. The equation you all throw around says 10 degrees, but (as usual) I am highly skeptical. Ive also wondered if it would have enough insulation to handle moisture long term until it became a sheet of metal without frequent dry out periods. As I am outdoors a predominate amount of time, I know this last winter there was a month where I would not be able to dry it at all without going into town and drying it in a dryer.
When I am on a UL kick, I plan on buying a 50 degree overquilt or bag. When I'm on my practical and comfort kick, I think perhaps I should get a 40 and play it safe. When I am on my reduce bulk kick, back to the 50.... etc....
This last winter, I had some gear stolen and was forced to use a 30 degree REI Kindercone that a friend gave to me over my MH Phantom 45 bag which I luckily had brought with me that day because I was trying to sell it online.
That January in Utah was the coldest on record, and I saw temps down (where I was at) at least to -5F. There were weeks where the temps did not go above 10F
Surprisingly, it held up decently good considering, but I had to dry out my 30 degree bag quite often which, to go back to my point, makes me wonder if a 50 would lose its effectiveness quicker if not dried often.
My overbag also developed quite a bit of mold, which I am unsure how it could of happened in such cold temps and my drying regiment, but I am no expert on the subject.
Im thining of breaking down and buying a Marmot Nanowave 55 at backcountry for $80 which would take the tinkering out of a quilt purchase and have often wondered about ditching my NF Asylum all together this winter and cowboy camping which I have never attempted in winter. I am worried of waking up with my synthetic frozen solid and not being able to pack it. Ive had that happen in a tent before, and its no fun.