I can't offer a belay, but I can say that apparently le gorge du tarn is fairly good in the high heat because you have good/easy access to canyons and the river itself, whereas verdon is bloody hot and you can't get to swim easily. (don't know about how hard the climbing is but it's supposed to be accessible and pleasant enough).
Spain is apparently, really fing hot during summer.
Have you considered the greek islands and/or croatia? I'm sure people will tell you the islands are good during the height of summer.
Chamonix? I know that at least the Aiguille du midi has some 23-25 350m+ sport routes...(on the backside of the telepherique station/point)