Yes, I have considered extra warm clothing. I happen to have a variety of weights of different high quality down jackets. MontBell lists the Superior men's down pants as $0. I think that means they are out of them. I did see some much more reasonably priced down pants when I shopped online, but not sure of the quality. I will have to read some reviews. Interesting the big temperature drop you were able to endure with the setup you described. I also happen to have a couple of pair of down booties, but I haven't used them at all since I moved from Alaska years ago.
Thanks for your comments Glenn.