Try to avoid fans that have cheap motor bearings.
This pretty much eliminates most of the fans sold at retailers.
Air king is about the best out there for clip on.
Temperature also affects humidity thus making it a critical factor. If your at 55% @ 80 degrees and temperature drops to 75 degrees your humidity will be 65%.
Drop a space heater in the dark cycle. Enough biomass and temperature drops will cause RH to spike while limiting dehumidifier efficiency. Powdery mildew would show up in that case.
Run a larger fan on a variac. Reduced fan RPM gets required airflow with much less noise.
Can always be turned up to compensate for increased ambient temperatures or bends and restrictions in ductwork.
Pulling lights up spreads yield but doesn't increase it. It's like growing a bunch of thumbs and popcorn with a light mover instead of some giant logs and a bunch of thumbs. I for one would rather trim the bigs than larf.