The biggest issue is that the peaches turn mealy on the tree. Just about all our late varieties will suffer heat stress like this if it’s really hot during ripening. This would be for anything past about +25 (Redhaven) The problem can be eliminated if the peaches are picked earlier and allowed to counter-ripen. Mid-season and early season peaches don’t get mealy, no matter the temps.
If it’s really hot, I’ve found some big varieties like White County, Laurol, and Autumnstar will start to rot on the inside near the pit. It seems like the really big peaches, the inside just seems to oxidize and the flesh dies, then starts rotting from the inside out, like a pear left on the tree.
Finally, some very dark red varieties (like PF 15a) get sunburned much easier if it’s really hot temps. The dark skin of the flesh absorbs more heat. If it’s really hot it will heat the skin up more and cook it.