No shame is bailing in those temperatures! That heat/humidity could get to anyone and big folks are not thermally "efficient". My wife and I tried a 70 mile ride on our tandem last spring on about the hottest day on record for that time of the year (over 100 degrees). Mid-ride couldn't get up a 3 percent grade. Finally, hit a patch of new blacktop which must have brought the temps up to 130 and that was all she wrote. Limped a few miles into town, found an air conditioned frozen yogurt shop and I took a cab back to the start to get the car. Be careful out there in those conditions.