Powdery mildew is the result of growing where the spores are AND having far too much humidity.... If you can't get your humidity down (55% is high), you are also risking bud rot along with the PM... Your grow looks, on the surface, to be pretty close to being ready to harvest if not harvestable right now (we'd need to look closely at the trichomes to be certain) - but, if this were MY grow and I was facing these issues, I'd chop.... If you chop when the trichs are milky (and I'm willing to bet they are from the look of the pistils), you'll get more of a cerebral effect from your smoke rather than a relaxing body buzz (if you wait until some trichs are amber) or couch lock (if they're mostly amber)... So your call....
Good luck!
p.s... and when you're done with the tent and they're all harvested, scrub it out completely and thoroughly with a mild bleach solution as you don't want ANY powdery mildew spores to infect your NEXT grow!)