OM - I think cold/wet vs. cold/dry is the critical issue for winter clothing. Decades ago, when I did 2-3 week winter mountaineering NOLS courses in Wyoming, it rarely got above 0 F in the day and went down to -20 to -40F at night. It was, however exceedingly dry and always sunny. Our clothing system was a lot like Jim's. I would ski in a wool union suit with a "flight jacket" material outler jacket and pants. Flight jacket material was WWII surplus - very shiny satiny but tightly woven fairly thick nylon - material supposedly used in jackets for fighter pilots. I would ski all day with this, a wool hat (we sewed on a rip-stop nylon cover for the hat) and NO gloves! Working ski poles always kept my hands warm. We got into camp, stomped out a tent platform (lots of activity there) and then immediately put on our over-sized felt mucklucks, huge synthetic insulated pants (fit over boots) and jacket with tunnel hood and fur rim and often put on a balaclava too. We had big double mitts. A quick dinner and into the tent! Reverse in the morning- did not get out of all that stuff until the minute we were ready to move.
I definitely was cold in the morning until I had skied about fifteen minutes.

When it is 5% humidity and -10 degrees you really cannot work up much sweat. I never skiied in my big over jacket or pants. I think I did have one light weight wool sweater that I could add if it was too cold skiing in long johns and wind suit alone. The snow was not wet - was like broken styrofoam pellets. Honestly, I NEVER took off the long johns, day or night! I do not remember ever being wet either. Any moisture from our breathing immediately turned to frost.

At the other extreme is my recent coastal hiking. Temperatures only vary 5 degrees or less day or night and hover around 60-65 F. 100% humidity and often lots of rain. You simply cannot stay dry so I do not even try. I do not layer much. I hike nearly naked under my rain clothes, maybe a very lightest wool t-shirt and nylon gym shorts. Dry fleece long johns, wool long sleeve top, socks, hat, kept in waterproof bag. In camp, I take off wet stuff and just lay it in the tent vestibule. Put dry stuff on and jump into my sleeping bag. Come morning I wring out the wet hiking clothes and start walking. Cold at first but soon warm. I use my old worn out rain jackets and pants that really are no longer waterproof - they act more as a wind layer/wet suit.

I still do the traditional layering system in the mountains in the summer and am gradually transitioning to only 2 light layers and one heavier down jacket. I wear my rain jacket all the time in camp as extra insullating layer and often backpack in my gortex jacket in the early AM - probably one reason my rain jackets soon begin to leak.

I agree with Jim - it bugs me no end to be bundled up in more than 2 layers. When I buy new stuff I always forget to have larger sizes for the second layer. That is one reason I like my down vest - warm but I do not feel so constricted.

I sure would like to dump the rain jacket when I am in the Sierra. I am sick of hauling it around when it may rain so little. And when it rains I usually just hunker out in the tent because I hate to walk in rain. Storms are generally short.

I love my new Montbell down sweater - it goes everywhere with me. It is a luxury! I doubt it would make a life-saving difference, but it sure is cozy in the morning when I get up!