My "hot side" stays at 85, and the "cool side" stays at 75. I don't use a Thermostat, I use a Rheostat. They are about the same thing except a Rheostat does not have a probe and it does not turn the heater on and off. The heater stays on all the time but with a Rheostat I adjust the amount of amperage going to it thus making it Heat more or Heat less.
I used a hand held infrared thermometer to actually measure the glass after it had time to heat up. It took me about 2 hours to dial in the correct temps, but ever since I got it set, it stays there. Every time I do a cage cleaning now I check the temps with the infrared, and so far they are remaining constant.