Which is more important later in flower - correct VPD or low RH?

My 5x5 tent hovers around 88° with lights on and other than removing a light from my tent I have no current way to get the temps down. It seems with my current setup I can have either the correct VPD with a humidifier set to ~60%, or the current ambient 48%, which will probably drop to 30 come winter. That leaves me with a VPD over 2.

So which is more important, keeping the humidity in the 40-60% range or the VPD below 1.8?

My 2c is that it doesn't matter what you do if you get mold, so I would personally put more emphasis on keeping RH down to the point I'm managing the mold risks. Yield be damned if you have to throw it all away.

I agree with @NewGrower2011 in that the rH is more important, like he said if it molds and you have to throw it all away, that difference in yield wont matter anyway. Gotta do what we can with what we have sometimes, I gave up chasing the VPD and just try to keep my rH in an acceptable range and I'm doing ok, no mold yet and still get my lb from 4 plants. Was going nuts trying to balance temps and rh and enough light without putting in ANOTHER ac smh, summer in the south is a bitch lol.

Yeah I have been trying to balance some of these factors myself, recently set up a 4x8 in some of my veg space to hunt some genetics in and ran vpd around 1.0 through the first 5 weeks of flower, lights on temps and humidity were 81-82f and 70-73% rh. Was not sure what to expect as its been a long time since I flowered in anything other than a sealed room with co2, ac dehu etc, but really enjoying the test tent so far. Anyways around week 5 I started to get nervous about the humidity esp during the night cycle, where it would hit 75 and cause the fans to ramp up. I am using an aci 6" for intake and an 8 for exhaust. I have them set on speed 4 as the minimum and it moves quite a lot of air through the tent even then but when they ramp up its like a wind tunnel. I have 5 or so walmart clip fans and a 9" floor fan in there also since I was worried about the high humidity with it being in the veg room. Even with all this airflow I decided to move a small dehumidifier into the veg room and positioned the intake duct for the tent right at the outlet of the dehu and this dropped rh inside the tent down to the 65-68 range where I am a more comfortable, but still fairly high. Some of the phenos in there are crazy dense so I am still a little worried avout mold but I think the amount of airflow being pulled through the canopy really helps. Its coming down next week so I will know for sure then but so far I havent seen any signs of it. I also sprayed the plants with regalia on day 3 of flower and have been using it in a drench every 10 days to further protect against mold.

TLDR ran 70+% humidity through week 5 of flower- 1.0 target vpd, tons of airflow and tent packed full of dense colas, 8th week now no mold.

this is my two cents unless you own one of these https://airrosshield.com/our-models/ id rather have a low enough relative humidity to prevent mold/powdery mildew from happening in flower you just never know if you have a super dense canopy there may be areas where the fan just cant get to underneath the colas and thats where mold/mildew/budrot will start

I keep my dehumidifier set to 50% in the winter. If you check the canopy RH it can be much higher than that, but under canopy defoliation and a strong extraction fan/good air flow can keep that from getting too high. Make sure you have good air flow across the canopy and below it-stagnant pockets are where mold will take hold. Botrytis also likes to take hold in damaged portions of the bud, so try to keep your leaves looking pristine and not all over nuted and gnarly, and also try to avoid any light/wind burn on your buds themselves. The ideal conditions for powdery mildew are actually cooler temperatures and lower rh-70 deg and 40 RH is where it grows best according to one study I've seen. The bigger threat is botrytis, if you keep your tent at 80 deg and 50-55% RH-which is what I use. If you have a weekly IPM program through veg, you aren't likely to see botrytis unless you grow very large, dense colas. You can avoid that by creating more bud sites in the canopy from each plant. If you want a smaller # of very large colas, then just know that botrytis will always be a risk no matter what you do, with some strains being much more susceptible to it according to genotype. A decent hepa filter in your grow room will significantly cut down on any free floating spores too.