I loved working in Greece. It was 40C+ but almost no humidity. We would work 6:30-2:30 until the sun got too hot, then back to process artifacts and paperwork, and swim in the harbour. Supper was at 8:30-9pm.
Here, like Suz and Glory, the humidity is what is punishing. We get a couple weeks where it does not cool off at night and is 30+ during the day with 80-100% humidity and it is awful. In general though I handle heat pretty well but am a sweaty mess. But I would say anything over 28C is when I would start wearing shorts or lighter tops.
My office is kept at 20C in the summer and I hate it because I can't wear my summer clothes at that temperature. I freeze.