I think Trailrunner has it--you're going to have to experiment to see if a VBL works for you. It does for me, but obviously not for everyone--we're all different!

A few one-night trips into frigid areas would be a good test--preferably close enough to your car that you can bail out if things go awry. I normally recommend the back yard (if you have one) as the ultimate gear testing location, but in your case, as in mine, it usually doesn't get cold enough!