Our elevation is approximately 850 feet. We live about 1800 feet at the coffee farm so we definitely feel the temperature difference when we go into the town of Kailua and then travel up Palani Road to the house to clean. It is a great relief to us to go up to the house. It seems like a good 10 degree difference to me — but again the moisture and stagnant winds down lower could be part of that.
Most homes in our area (our neighbors at our same elevation) do not have air conditioners. It would be recommended at lower elevations because of the humidity and temperatures. Closer to the ocean and the moist air from the ocean will combine with the higher temperatures to feel muggy. Tolerance for temperature differences will vary from one set of people to another, for example someone who comes from Arizona versus someone coming from Alaska. And the wind movement will also affect how comfortable you feel. The majority of the time we have very good airflow and the house is designed to accommodate air with all the windows it has (we just spent two days cleaning windows up there — I am freshly reminded how many and some are way up on the peaks).