Not that I would ever choose to be on a trip in this kind of weather, but the cold snap gave me a chance to see how my gear would do in extreme (for me) conditions, from the security of my backyard. Forecast was for 5 below, light winds, and we already had about 4-6 inches of snow on the ground. Actual air temp got down to -9 with a -13 dew point.
Tent: Six Moon Designs, Lunar Solo (vestibule rolled up)
Bag: Montbell, U.L.SS.Down Hugger #0
Pad: Big Agnes, Insulated Air Core (rated to 15°), full length, rectangular.
Pad2: Thermarest, Z-Lite (cut for torso only) for added ground insulation.
Clothing (while in bag):
Top: Icebreaker Hopper T (short sleeve) and Icebreaker Rock Zip (long sleeve), no jacket
Bottom: REI Saharas, nothing special, no long johns.
Feet: Thin Smartwools socks
Hands: Thin fleece liner gloves
Head: Loki balaclava, Buff, and Icebreaker Mogul Hat (I wear a lot on my head as I roll around lot and my head comes out of the bag)
Nunatak Down booties on feet while setting up the tent (not worn in bag). My feet felt completely comfortable in the Teanaway booties, not even a chill.
The ground was rock hard and I had to use a hammer to get the stakes to hold (good rock would have done the trick). The MSR Groundhog stakes took the pounding well. The stakes were hard to get out of the ground in the morning. It made me wonder how some of the lighter stakes would handle the abuse.
To my pleasant surprise I wasn't even chilled throughout the night. I tend to sleep warm but thought these conditions could be a problem. The Montbell bag is amazing. The added Z-Lite pad (torso only) under my Air Core gave good ground insulation. Added insulation under my legs was not missed. The Lunar Solo iced up with some condensation, and given its limited head room, led to some ice bits on my hat and bag once I moved around in the morning.
My main problem was getting my head covering, and position in the bag just right, for comfortable breathing. I had the balaclava on. I could pull the Mogul hat over my eyes and nose to keep them warm (I tend to breath through my mouth).
The air was just so cold to breath. I tried pulling the Buff loosely over my mouth but that felt claustrophobic. It was a tough balancing act to keep my face warm but also allowing comfortable breathing. Breathing the cold/dry air also gave me a sore throat, which I still feel now.
The experience was a good one. It gave me the confidence to know that my gear was good to those temps (granted that there was little wind). The cold air making breathing uncomfortable was a bit of a surprise.