For my sub-zero long runs, I only do one tech long-sleeve top, short sleeve tech on top of that, and fleece sweater turtleneck above that. Tech-short-shorts (no underwear) and then tech pants above that. And that’s all I need for core. After that, the key things are then ear and hand protection. I do 2 to 3 layers for the ears/head (usually 0-degF is my benchmark for adding that third layer,) HEAVY gloves for anything below 30-degF and then I add another light glove below that sub-zero, and then I add a second pair of socks if sub-zero. The cheeks get cold, but I find the first 10 to 15-min are most uncomfortable, but then it goes away, and I haven’t gotten frostbite yet in minus 25-degF and counting… So I think that part is mind over matter.