Year-round in the Southeast, mostly Alabama and Tennessee. Some early spring and late fall trips out West. Temps rarely reach below the upper teens for either, though we got a couple weeks each of single digits and ~0F here this past winter.
The last several years, I've used three Marmot bags, a Trestle Trails that is just a shell with DriClime liner, plus their 800 fill Arete and Pinnacle. Also use a Sea to Summit Reactor liner during the warmest weeks.
As an exceptionally warm sleeper, the 40 degree Arete is good into the 20s with midweight baselayers for me, and saw the bulk of my use, with the Pinnacle usually only coming out when the temps were 20s or less.
I've switched to quilts for comfort, weight savings, and also because I tend to burrow and breathe into my bags.
Now have two quilts, the 6' Wide Katabatic Palisade, and a 72"(for up to 5'9") Wide Underground Quilts 50F Flight Jacket, both with 850 fill Hyperdry down.
The Palisade is rated for 30F, but with baselayers is more like a 15-20F quilt for me, and has worked down to 0F with heavier bottoms and a down jacket. Hasn't been used, yet, but I recently bought a Goosefeet hood from ZPacks to use with it.
So the Palisade is for 0-50F, while the UGQ quilt is for anything ~50F or above.
I'm keeping my Marmot bags for loaners, and for when/if my girlfriend gets out with me, but the two quilts do it all now.