We had a couple weeks of temps over 100 here long before the weatherman went all crazy about the current midwest heat wave. I can tell you, when it's 100 to 105 or more, and the sun is baking the road surface even hotter, any long rides will really fatigue you. Yesterday I did a hundred miler down to a little border town and back, just for fun. Not too bad, this week it's cooled off to a mere 98 or so.
As for the border town, all I can say is, if ever a town didn't have a reason to live, that's the place.