My experience with using RH was completely accidental and due to the way in which my garden became infected (via my visiting son's clothing), the fact that I wasn't running very good ventilation and was much more concerned with keeping the room warm at that time.
In any event the RH in my flowering room during winter stays well above 50% most of the time, it's usually in the 60%-70% range, and during flood days (now that I have trays) it hits 80% easily. But in my veg-table (a raised box on wheels, sided with reflective-coated OSB, lit w/a combination of shop lights and CFLs) it's usually 50% or below, and that's where I discovered mites several weeks after my son visited. And in the worst way, by discovering stippling, looking further and finding webbing.
For some reason they never got a foothold in the flowering room, and since then I've made it a rather strict habit to always visit each area in one direction, i.e. I visit the flowering room first, ALWAYS, and then open up the veg-table. Everything's easier to treat in veg, so that's where I'm more willing to place risk and try stronger Txments.
I know a lot of people say you're risking bud-rot and mold in the higher RH values, but my girls love it, and the only reason I have PM in either area right now is because it established during summer in a nearby veggie garden (which was also pretty badly infected with aphids). I've also suffered PM at lower RH values, and have seen it persist at values as low as 30%. I know that's not the only issue, just as I know that someday I probably *am* going to see bud-rot or some other problem with the higher RH (just like I'm having RA problems for the first time ever), but for now I watch 'em like a hawk and try to learn as best I can.
Give me more grows under my belt and I may become more equivocal about it, maybe not. I know Jalisco Kid likes to run his rooms at a higher RH, though, and I believe he's got plenty of seasons under his belt.
