The Flight would be warm enough as part of a layering system as would RJ's hooded version of the Cocoon pullover. I personally use a Cocoon or a micropuff over a midweight merino baselayer and under a W/B shell or over my lighter softshell jacket and I'm good sitting around in the teens.
Is experimenting with the RBH VB shirt on a multi-day trip appropriate? I would field test it on a day trip or 2 before commiting to it. It's one thing being on the bleeding edge of product development, another being on the frostbitten edge. However I know Ryan is capable of extreme gear testing as witness RJ w/ the Vapor Mitts---
"We had the privilege of testing RBH's flagship product, the Polarguard 3D-insulated Vapor Mitts (Figure 1). During an Arctic cold front that passed through Montana this winter, we were pleased to test the mitts during a front-porch bivouac at 27 °F -- below zero. I donned an expedition down jacket, slid into a winter-strength down sleeping bag, and cinched it up around my armpits so that my hands and arms would remain free. I slept on a closed cell foam pad and sealed myself up in a Pertex Endurance bivy sack. Thus, the only insulation between the skin of my fingers and hands and the brisk outside air was that provided by the Vapor Mitts. I lasted about six hours in the cold before the ice on my face mask began to interfere with my breathing, so I called it a night. However, the Vapor Mitts kept my fingers comfortable and they never went numb or even felt cold."
If The RBH shirt is long enough to cover a pair of VB pants it might work for digging out a snow cave (?)and together w/ the VB sox could be used inside the bag. You add up the collective weight--don't be so tied into base weight alone. Comfort wise, I would rather have merino or capilene against my skin and don't relish the idea of working hard even in the low temps. being considered, wearing a VB suit.
I chopped wood one winter in such conditions and tried a variety of clothing systems for the job, including wearing a Stephenson VB suit. I was warm but wet using it, and eventually chilled. The classic metablolic stabilization that is supposed to occur w/ VBs did not happen. The most comfortable ensemble I tried was wearing wool (Filson---pre-merino days)--I know, so trad. The VB suit concept also underwhelmed me on some winter mtneering trips. VB's have always worked best for me as a VBL in a bag in appropriately low enough temperatures. In fact they are a winter must-have in my kit.
In Winter I have always used a canister or white gas stove but then I 'm almost never solo in Winter so it is the lightest solution for 2 or more. I own esbit and alcohol stoves but do not consider them practical for the Winter use I would subject them to--- melting snow and making lots of hot soups and beverages.