Try Awseomeminer firmware it's vnish firmware with added features, using their version you get to use their monitoring software for free, which I think is very useful for your set up.

What I would do is set a high profile, something 20% below the PSU's limit, and then use the monitoring software to play with the mining profile based on the temps, here an example.

If max chip temp is < 85 ( keep 52th profile)
if max chip is > 85 , ( change to 50th profile)
if current profile is 50th and chip temp is >85 - (change to 48th profile)
if mining uptime is > 2 hours and temp is below 75c and profile is 48th (change to 50th)

These are some of the many things you can do with Awseomeminer firmware, you get also get it to send you emails or telegram notifications for when something happens, the initial tuning for each profile can take a while, but when it's done once, it's done for good and switching from one profile to another will take only a few seconds, this way you can run your miner at lower hashrate during noon when it's hot, and higher when it temps cool off a bit at night.

Ha... at your own risk! I'm only giving you the info I observed in the past, and I didn't look into it further to get any definitive answers. I'd suggest doing your own experiment to verify what I saw. You can run stock firmware immersed if you have some fan spoofers. If you run stock in the same setup and the temps come out to be 10degC lower, then make your own conclusions...

The chips were designed to be run hot, the temperature delta to ambient is needed to move all that heat with air cooling. So you can actually run into some problems if you run too cold, timing on the ASIC design is very complicated and is temperature-dependent. So if they designed the chip for say 70degC to 90degC range, it may not meet timing requirements at 65degC for a given frequency and voltage.

I'm sure there's a sweet spot that would be below 80degC, but you'd need to experiment on that to find out. My point about the 80deg target on factory firmware is only that Bitmain seems to think that their chips are happy at that temperature.