I usually put the AC on 76 during day and 74 at night.
I run the heat at 68 during day and 66 at night.
So personally, I know I sleep ok between 66 and 74.
She insisted all we need to do was open a window, but I felt like if it really was 75 out at 10pm, the open window wasn't going to cool down the house at all in a short period of time. A quick blast of AC (set un 74, it's not like it was going to run all night), however, would.
I went on vacation with my brother last September, to Arizona and Utah. He insisted on running the AC on the airbnb and the motel suite at 60, because "that's what people sleep best at" and "I don't care about the energy, I'm not paying for it." As soon as he as asleep, I would sneak to the thermostat and put the AV on 70 or something more reasonable than 60.