I'm starting to push what I can do in a day, distance-wise, and am starting to think about what I should carry in terms of insulation for unplanned overnights (3-season conditions) in the White Mountains of NH.
For a bit of context, I did a survival class in NH where I deliberately slept in slightly sweaty clothes after not eating all day in just a SOL bivvy to see how bad it got, and I was quite cold at ~45F. I made it thru the night, but it was rather unpleasant. If I was in a real survival situation (lost, wet from rain, dehydrated, etc), the extra warmth from some kind of insulation might make a big difference.
I already carry silkweight wool thermals (top & bottom) in my emergency kit, and typically carry something like a Rab Xenon (summer) or EMS Down Ascent jacket (winter).
The Sea to summit Spark SPL 45 is attractive, as is the Nuntak Arc AT, but is there anything else I should be considering? A lower-body version of the Xenon seems like it might fit the bill for "survival" level insulation given what I already carry, but I think sleeping bags/quilts provide more warmth for the weight and are more versatile.
Price is less of a factor than weight, size, and resilience to being compressed, as this would be a "carry every time" kind of item, so it would see a lot of stuffing (approximately 1x/month)