Regarding WPB in cold, cold weather,
I guess I should have clarified, the original post was geared more towards standing around camp, and my reply was for activity.
Lets say for example you are exerting yourself at -10 to -25 F and maintaing your body warmth, the temperature gradient across your insulating layers is very steep. At the end of that gradient is your gore-tex or whatever you choose to use, at this point the fabric will be freezing as well since it is in contact with the cold temps. The pore spaces in the fabric will freeze with moisture it is trying to transfer inside them rendering the jacket an icy shield. I've had many fabrics, from standard Gore-tex, Gore-tex pac-lite and even a regulator soft shell - the Kru-shell, freeze INSIDE when exerting in extreme cold. It sucks! imagine wearing a sweaty fleece with a shell of ice&frost, then an outer shell, while trying to stay warm at those temps.