I must be different, as heat doesn't really bother me. I just got back to Denver from central MO today and temps were in the 90s all day, no problem in 730 mile ride. I wear the full Aerostich Roadcrafter suit. Seems retarded to be fully covered with a suit in hot weather but it works better than having hot air blow on your skin, trust me.
I'll admit the humidity makes it worse, but not that much. Riding at 110 dregrees is hotter than riding at 90 with a 110 degree heat index for sure. Don't know where the heat index thing was invented, but it's way blown out. Heat index was 110 in MO and it wasn't anything that major.