For what it's worth, mine runs from a low of 90% to a high of 99% all the time. I don't think really high humidity is a problem as long as you have lots of air movement (constant). I have 1 large DC fan running 24 hours a day blowing so the plants move about and a second that runs through the wall when I decide to run it manually. I get very little mold. I get lots of roots and lots of happy orchids. You are correct, though, it depends on the species you select. Humidity seldom drops below 80% and then only when the through-wall fan is on.