I keep ours at 76˚, the house humidity is around 40 to 45%. Before we got this system (Trane Variable speed) I used to keep A/C at 72˚, but with the variable speed we get better humidity control, so 72˚ is getting cool.
If it's really hot out, I bump it up to 78˚ to help out the power company, and I don't like the big slap in the face when I go outside.
A/C running colder than 70˚ and outside tempts below 50˚is not good for it unless it has a "Cold Weather Kit" on it.