Can't see this going unanswered.
My advise would be to go "uninsulated" but large enough to put any anticipated layers under. I did just that a few years ago. I bought a parka From Gray Wolf woolens. It has elastic cords around the waist and hips and the bow arm so I can snug up the garment when worn without insulation or let it out when I'm wearing many layers. You'll have a lot more versatile garment if you go with a plain shell.