Which is why I did the testing in my front yard; I wanted somewhere to bail if things turned out to be colder than I'd thought. I was
expecting an uncomfortable night, since I was testing the low end of survivability with this under insulation rather than its comfort zone. However, the cold I experienced was farther out than merely uncomfortable; it was not something that I could sleep through, even fitfully.
As to the HHSS vs. a PLUQ, I'd expect that in terms of raw warmth (i.e.: no wind, no precipitation, low humidity) that a no-sew PLUQ and the SS without a space blanket would perform about the same. I'd also expect that the SS would perform better in wet, blowing weather; while the PLUQ would perform better at high humidity without precipitation or wind.
I would also expect that the HHSS with
a space blanket would perform about the same as a sewn-up PLUQ with average added insulation (I'm assuming InsulBright or a layer of IX with the proper darts here) in terms of raw warmth. The HHSS should perform better in wet, windy weather; while they should be about at a draw for high humidity, since the space blanket will act as a vapor barrier to prevent the OCF pad from becoming soaked.
As to fit, it works almost perfectly. I still need to add Demostix-inspired draft skirts to my hammock to close up the ends of the poncho (since I used OmniTape [well, the generic knockoff of it, anyway] as a closure system for the poncho, it doesn't grip quite well enough at the ends for the shock cord there to not be able to pull it away from the hammock body when I shift position)--and the ends of the modular underquilt that I'm designing. Once I do that, it should seal up nicely.
There'll be changes on the whole thing as I get time, inspiration, and funds. One thing at a time, though...