I'm just about to order a new 0* Incubator.
I would say my average night time temps are 20-40* but I'm often exposed to the wind. I would also like to go with a 0* because my wife would enjoy it more (especially if I carry it in my pack)
I also get out in the winter and would use it quite a bit.
My 20* Incubator serves me very well and I've had it out to 23* with comfort. The 0* incubator will be just a little more insurance, a solid dedicated winter quilt which I could vent and another piece of gear to help outfit friends who travel to come out with me and want to opt to use a hammock instead of a tent.