I have enough nights well below 0 to know I would rather not use the VBL unless I needed it to maintain a dry bag. Back in my 20's and early 30's I hung out with a bunch of folks who did quite a bit of winter stuff in the Adirondacks, NH and CO with a trip Denali and one to South America. ( I did the did the Denali trip, but not the SA trip) In the Adirondacks or NH nights below -10 were the the norm. Maybe it was just our group but none of them used a VBL except when we thought we needed it for moisture management. Its possible that our group was unusual in our equipment choices, or times have changed.
My original winter bag back in the day was a marmot cwm (with the Gore dry something shell), I followed it with a WM Puma which I still have and now I also have a Marmot Col which came from a friends estate. The CWM and Puma will keep me warm even after several nights out without a VBL.
I don't do as much of that stuff as I used to, my old friends have moved onto other activities and I am not in the shape I was at 30. Its possible the equipment tech has changed. back in the day we all bought super warm bags ( or so we thought) even if they were heavy, in fact a lot of our winter gear was pretty heavy. Perhaps a lighter bag with a VBL is more the norm now. Its also true that the weather has moderated. 30 years ago overnight lows in the NE mountains of -20 to -30 were not uncommon. in my last few winter trips its been above zero, heck least year I did a couple of the Adirondack peaks and I took a quilt not a bag.
