Its all based on your conditions. Altitude, normal relative humidity in the area, ect. Somebody in florida (or even myself in ga) has a much higher humidity than somebody in say arizona so while 75% works for them 65% works much better for me. Temp just depends as well. My normal humidors sit at my basement temp of 67-70 but my wineador is at 64 all the time. Realistically you just want to keep it below 70ish to keep any beetles from hatching and not so cold it dries out or becomes brittle.I always thought 70% was just about right? The magic numbers were always 70/70. 70 % at 70deg or there abouts.
Mike
Its all experimenting to find that balance and obviously you have to use a good humidification device along with a properly calibrated hygrometer.