I have to agree that 4 layers can get constricting, but might be ok for a long slow trudge as a contingency plan if you get hit with a rare extreme. We don't get -30F that often, but on a long trip in December/January/February it can happen. If you have a loose enough silk layer you can slip it in between your wool underwear and 200wt fleece pants or heavy wool sweater, then your shell layers, and that can work well, for the rare extreme. The silk can help trap air and keep things sliding. No layers should compress other layers though. That's just wrong. I tried the silk top over my medium wool sweater and it really didn't work. Maybe if it was XXXL. Blousing can help also, but doesn't work unless stuff is loose and well matched. I don't even think the skin layer needs to be stretched on. Just a little slack and clingy is better for winter, I think. That's really just 3 layers though, unless you count the shell layer. I've done 200wt fleece over my medium or heavy wool sweater, but that would be too much with 2 layers under. I've used a knit wool vest as a 4th, and flannel boxers as a 4th, and that can work for a long slow trudge but its all gotta fit loose, and it has to be only as a contingency plan for the rare extreme, and then you delayer from there for expected conditions. One of the top layers and the top shell should overlap also, at least to below the butt. I have an XXL 4oz wind layer for winter.

I would have to agree however, based as much on my lack of experience as my experiece in such prolonged extremes, that if you are planning on -10F to -40F for the better part of a several day trip then you really want to think about down parka and pants with 2 wool layers underneath, one thicker and looser than the other so that you could wear either one or the other or both. But for the stuff I do, mostly above 0F, and very often wet, so I don't carry any down clothing, but I have all my layers matched to fit loose but airtight if I do get hit hard with a cold air outbreak. I just love a good long trudge home in the cold.

I'll have to post again when I get a chance to try all these layers out.
I just got my silk this year and haven't tried it in really cold stuff yet.
I think getting the sizes and spaces and blousing just right is critical.