Disclaimer: This was for personal testing purposes and nobody else should try this.
I'll be doing some camping in Colorado some time soon and we have to take a tent because we'll be camping above treeline a lot. I have decided to use a Hammock Gear Burrow. My girlfriend and I both have Burrow 40's, but she recently got her Burrow 20 to use out west at higher altitude and in colder weather. I also ordered a Burrow 20 but haven't received it yet.
We got a good amount of snow and ice here in NC last weekend and she wanted to test out her Burrow 20, so we set up our tent (Big Agnes Fly Creek 2) in the snow (mostly ice) and slept outside. Temperatures never went above freezing and dropped to 24 degrees as a low.
BA Fly Creek 2
Thermorest small sleeping pad (1 inch thick)
Zrest (cut down to 6 folds to fit the torso)
Arrowhead Equipment 3 season foot pad
Hammock Gear Burrow 40(+1oz)
Sea to Summit silk liner
OR echo short sleeve shirt
patagonia cap 4 hoody
OR Filament down jacket
cap 2 bottoms
REI lightweight merino wool socks
This is the clothes i would have in colorado (might trade out the down for synthetic midlayer). This is the equipment I am taking to colorado except i would not have the zrest, just the prolite pad.
I had my doubts, but i stayed REALLY comfortable all night. The only reason i woke up was because my feet were a little chilly on the footpad. I could feel the ice below me melting where my heels touched the pad. other than that, the Burrow 40 did great. A few factors probably helped here...the tent is small, there were 2 people in it, and I was sleeping beside of my girlfriend who was wrapped inside of a Burrow 20 (she didn't wake up at all). My girlfriend is a cold sleeper; she had pretty much the same clothes on as me and she never felt even a little chilly (she did say she could feel the cool under her feet when she woke up that morning).
I feel confident that if the temperature drops to 30 degrees and I had the right clothes i could trust the Burrow 40. If i had a full length pad i could have gone a little lower and still slept comfortably. Winds were calm so that may have helped us a little also.