A study of wild Fox snakes in a man-made hibernaculum showed that the snakes move during hibernation to maintain temps between 45-50. I hibernate an extensive collection including Mexican brown vine snakes, Northern water snakes, gray-banded kings, eastern kings, Aesculapian ratsnakes, subocs, garters, racers, coachwhips, alligator lizards, desert iguanas, horned lizards, regal ringneck snakes, Sonoran Mt. kings and all the Eastern United States rat snakes.
I find that animals are up and moving at 50 degrees. If the temps do not go lower than that, my animals start to lose weight. I have best hibernation at 44-47 degrees. The warm weather animals like racers are torpid at 50 but cold-tolerant forms like garters are active at 47.
Gray-banded kings are members of a cohort of species which includes the Mountain kings and upland variable kings from Mexico's Sierra Madre. They are about medium in cold tolerance in my experience.
A fellow herp keeper likes to hibernate his animals around 35-40, although his collection is not so extensive and includes mostly northern species like water snakes and turtles. The Midland painted turtle is the most cold-tolerant American reptile, and remains active under winter ice, rarely being taken on hook and line by ice fishermen. Hatchling painted turtles remain in the nest over winter as the ground around them freezes solid, to awaken and emerge unharmed the following spring.
I've had good results for over 30 years with hibernaculum temps in the upper 40s to low 50s.
