I can say, subjectively, that I don't feel any wind through my Patagonia Ascensionist, whereas I did through I couple of membrane fleeces that I tried and didn't like before.
I love my Ascensionist. I view it as a contemporary equivalent of the old canvas or ventile anoraks - although less of a catastrophe if it gets wet. Or as a kind of heavy duty winter windshirt: with a base layer or two under it, I find I'm fine for pretty much anything as long as I'm moving, and when I'm not moving so much I have room under my size Large (at 6' and 180lbs) for a fleece or a down sweater if I need one.
It's definitely not a garment to carry: I only bring it if I expect to be wearing it most of the time.