All I know is if I get to the point I am cramping, not just light spasms, I am entering heat exhaustion as well and need to take a long rest under shade, drink at least a liter of both water and electrolytes, and douse water on my head/neck. I no longer will ride in temps 90F+ and will ride in the early morning to avoid summer heat. My tendency is to push myself and after my last episode of heat exhaustion, it is just not worth dying over "one last climb." There's no money in it.