I tend to around 80 on climbs. Too much lower & I really can't stand it. Any higher I find myself looking for another gear. The trick is to find the balance between cardiovascular and muscular systems. Hill climbing is largely about technique. It's a skill. If I'm down around 75 I don't have the right gears or I'm not on the right hill. Low rpm/high torque is hard on your knees & drivetrain. No one at the gym is doing 10 minutes of continuous squats, deadlifts,or leg presses. I don't think I should be either.

88-92rpm seems pretty average for flats just as a matter of habit. Maybe a touch lower if I'm fatigued or just not paying attention.

YMMV