I would suggest reading this article
The Science of Warmth. In essence, the problems with extremities in the cold are often tied to an insufficient protection of the core, not of the extremities. If the core is well protected, the insulation needs for the extremities drop.
I read it, but think I disagree. IME, if your hands/ears/feet are warm, your torso will be warm; if your hands/ears/feet are cold, your torso will be cold. YMMV