Craig, I'm in NE Bama and hike a lot on the Cumberland Plateau, so probably face pretty much the same conditions as you temp-wise. For me, the Nanopuff is shoulder season gear. When it gets "soul-sucking" cold as it can occasionally in the SE, I turn to a real down jacket (in my case a WM Vapor). The Montbell isn't going to be enough for you when it's real cold unless you use multiple other layers. The Bitteroot however is something you can throw on over whatever you hike in when you stop moving, and you'll be warm. As cheap as those can be had, that would be my choice in your shoes.
This past week I hiked in wintry mix getting down into the 20's....while on the move, my Icebreaker 200 top and Capilene 4 Hoody were plenty adequate, but as soon as we stopped it got COLD- it was gusting 30+, and with my Vapor (which has Windstopper) I was toasty.