This might be miniority opinion, but being an old Elk Hunter from Colorado all of my experience has to do with layering in cold weather.
About 20 or 25 years ago I heard about this guy in Grand Junction that was making what was alleged to be the best sleeping bag you could buy. He had developed a material that didn't absorb water like Goose Down and actually was very close to Goose Down for insulating properties. I checked him out...he has an outstanding web site
www.wiggy's.com that contains all sorts of cold weather gear and information.
Besides buying two of his sleeping bags, I bought, and have used extensively on the various bikes I've owned, what he calls a "sweater". It is actually a jacket made out of his Lamalite insulation material (the same material he uses in his sleeping bags). It works great in filling all the voids between your body and your outer jacket. I have used it with a Roadcrafter one piece, the two piece Roadcrafter jacket along with my current favorite, the Darian jacket. If you can stop the wind, this so called "sweater" will so the rest....I've ridden year round in New Mexico with this set up and been just fine.
So, if you hunt the high country you might want to check out his sleeping bags, and for great insulation on the bike or off, his Lamilite sweater has served me well.
Although I have been to Grand Junction a number of times, I don't know the owner and have no realtionship with Wiggy's other than being a very satisfied customer.
Long Distance Rider