Get the right combination
I used to carry both a solid and mesh jacket on long trips, but now I have an Olympia mesh jacket and Motoport kevlar pants, both with removable waterproof and insulated liners. This way I carry only one jacket. The waterproof liner is a good jacket and the insulated liner was discarded in favour of a good fleese that can be used on the road as a sweater as well.
Now I'm cool, warm and or dry with less gear.
Kudos for Olympia "Air Glide" mesh
I've got an Olympia "Air Glide 2" jacket and pants (wifey has "... 3" version). Their mesh has proven very versatile, and they come with water-resistant and insulated liners that greatly expand their climate wearability. In a recent ride in 102??weather, the mesh was a perfect "top cover" to an evaporative vest (wet T-shirt will do, too): the combination provided excellent comfort with the mesh allowing airflow. (I'm in a dry climate, so works well. Humid climates would be a very different kettle of fish.)
Additionally, the reflective stripes and high-viz colors available from Olympia are resilient even through multiple washings. This has saved my a** a few times.
Hot weather, High humidity Jacket
This works best for me at temps above 93 degrees in the deep south with very high humidity. Take a look !