I'm from the DFW area, with moderate humidity. I've been to Houston in summer. Going outside in the morning was like walking into a pool of hot water. Afternoon didn't feel quite as wet, but it was hotter. It's definitely worse than what we get (most of the time, we had some days with a 115 degree heat index early this summer because it was raining so much).
The worst to me is low humidity. The deserts in west Texas usually don't get extremely dry, but I've been there when it happened. Temperature of 110 and 2% relative humidity, my eyes were watering, my nose was running, and my throat was dry (just like what happens in the cold), and the bare ground was baking, reflecting the sun's heat, so it was like the sun shining from above and below. It hurt. That was over 15 years ago when I was younger and heat didn't bother me, but it still hurt. I think it's because I'm accustomed to the semi-humid weather of my homeland and the semi-dry conditions the Texas desert get normally, but that was my first time in very dry heat.