Hey Keith,
I have also tried it with Green Rats and Sinaloan Milks with no success. There was no difference in size, only a longer incubation period. I don't think it was meant to be for those species. It only seems to work so far with montane kings (pyros, mexicana complex, ruthveni and alterna). It doesn't make for larger adults in the long haul. The babies are just larger and heavier at hatching which I think is a plus on both counts, those that do feed right away are big enough to down pinks with ease, those that don't start feeding right away have more stores for winter. I think it is the way it was meant to be. I started doing the lower temps on the theory that nobody ever finds pyro eggs because they are layed underground were summer temps are usally a constant 72-73F. (the average prefered body temp of foraging pyros has also been found to be 73F) I also noticed over time that the hatching time for my babies and the size of my baby pyros were the same as hatchling pyros I was finding in the field. On the other hand, pyros hatched by my friends at 85F were smaller(often MUCH smaller)than the new babies I was seeing in the field.
For common kings I think I would stick with the tried and true temps. If you were going to put non feeders down for the winter I would make sure not to do any force feedings prior as that would kick in the metabolism and start burning needed calories.
Rich