I can take riding in the low 90s when there's no humidity involved. However, that's practically never here. I used to just head to the gym when it was really hot and humid, especially when there's an air quality alert. Now I might ride early in the AM, take a hike/mt. bike in the shady woods, and go to the gym. I've done a few hot and humid rides this year; it takes me a few weeks to acclimate. Basically, though, I develop headaches in the summer when it gets like that and I try to do too much.
My range for really comfortable riding is pretty narrow! I do best between 58 and 72. Personally, I couldn't live without AC. But, I think my definition of comfortable AC is different from most of the people in New England. This comes from years of living in the desert; we keep our AC set on 78. In AZ, we kept it at 80 or 82. Most people around here keep it on 70! I would be freezing. And a lot of the time, it's on to keep the humidity out. I have mold allergies and once that gets into the house, I'm dead.