I can't say I find any increased benefit from training in hot weather. I live in one of Europe's most visited tourist beach hotspots. We have Sunny days for over 300 days per year. Temps are pretty mild which is a big attraction for cyclists but July and August hit 90-110F frequently on the coast and more a little in-land where we ride to.
I grew up in Durban, South Africa which was warmer, more humid.
I'm doing 5 hrs tomorrow with some friends, 2 of which are UK tourists. We'll head out at 7h00 to avoid the worst of the heat. I need to hydrate more in the warmer weather and I do like Summer here but I also avoid the worst of it for training since I have been out in it often enough on long rides to know I don't feel any benefit from it and risk sunburn.
