Eh, studies conflict with each other. Hard to say exactly where is best, but the quick sweat release at the higher temps really seems to help with the removal of toxins. Our sauna record is 240, but I wasn’t there that day. I’ve been in at 220 multiple times, and that is brutal. Have to hose the benches down with cold water just to be able to take a seat. 200 is about the max relatively comfortable temp for me. And yes, from an honor perspective, we only sit on the top bench.
I recall one of my junior high friends did his science fair project on body temp in saunas. His temp got up to about 105 - I wouldn’t want to go too far above that. (He’s a Finn, so I’m guessing his sauna was in the 185 range).