75 is perfect for greys... you want it between 70 and 80 during the day and a little cooler at night. I wouldn't worry about the heater ... you get up near 90 it isn't going to be nice anymore. Mine sits between 74 and 76 dureing the day and they are happy active froggies perched up by the light while sleeping. All I use is Exo terra repti glo 2.0 bulbs