Yesterday just happened to be right at the 93-degree threshold and I had my usual vented jacket (not mesh) with safety vest over and it was hot, but not unbearable for my 30-minute commute. The vents seem to provide enough air movement to provide some cooling by evaporating my sweat, but not so much as to dry me out. I was pretty soaked with sweat by the time I got home. One thing everyone should try is a white helmet, which I think helps a lot. Also, I suspect that helmet cooling is very important and that is where a lot of gear falls down. I know my helmet is deficient in the vent department. I personally do not like to ride without a full-coverage helmet and face screen. I wonder if manufacturers could make some sort of small water reservoir in the helmet that gradually fed a layer near your skull which would then evaporate and cool your head, and therefore your whole body?
For my part, I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to move. Robert Louis Stevenson