What temp bag would you use

Brian,
I'm from Pittsburgh but do most of my camping in WV. I typically change over from a 20 degree bag to a 10 degree bag (a Versalite) by the
middle of October. By January I'm into a zero degree or heavier bag. Most of my camping is under a tarp or a bare bones set-up (fly, poles and ground sheet without the tent body) in really shitty weather and I'm getting older (so colder). But even back in the 70's I always used a 10 below bag for winter trips up to Potter County (used a tarp back then too). I'm a firm believer in over bagging; when nature decides to pound you into submission, it's nice to have a bomb proof cocoon to retreat to.