"How do you like the Pertex Endurance shell for the Blackwelder? Does it get clammy or does it breathe ok?"
I like it fine. It seems perfectly breathable and the inner shell is snuggly soft. I don't think I can really comment on clamminess though. In subzero temps I'm usually wearing a VBL jacket and pants which will far overshadow the quilt in terms of any breathability issues.