The max HBM temps are mentioned in the bios on techpowerup:
So 95°C seems the critical temp.
The higher you go in temperature, the more difficulties your HBM seems to have with it’s timings.
At 60°C my cards have close to 0 rejected shares per week. At 70°C they will throw a few per day. At 80°C even more.
Some say also that the longevity of the HBM degrades with higher temperatures. Some say to keep it below 80, some below 70, some at 60°C. Lots of different opinions, no facts.
I think it is something that you’ll need to evaluate for you personal. Do you want to invest a lot of money to get their temperatures down? Or are you happy with a few rejected shares at high temperatures? Or are you more happy with lowering the hash rate by lowering the wattage and the clocks?
I’ve also repasted a bunch of cards which helped a bit in their temperatures; some (not all) went down 5 to 10°C. Here outside temperatures are now also +30°C so the cards are sweating a lot and I can’t get them below 70°C anymore, some are running even around 80°C. I can’t imagine what temperatures those cards would have been if I hadn’t repasted them!