The IBA, which knows a thing or two about riding in all different conditions, published a detailed report about mesh and temp. Long story short, anything over 93 degrees F and one will ADD heat to the body when riding while exposed to the airflow (mesh). P14 above has it correct.
Having moved to AZ I'm in the process of learning how to deal with 100 degrees plus on a motorcycle. The learning curve is extremely uncomfortable!
Using LD Comfort stuff right now trying to refine what's needed.
Mesh up to high 80's and then a shell with the LD stuff. We'll see how it goes. My friend Moshe Levy, who writes for just about everybody in the States on a freelance basis had a very favorable review a while back in the BMW MOA publication. He knows his stuff well.