I also try not to ride in the 90's. I am going to do a group ride Wednesday, where it might be 90, but it leaves from near my house and I can ditch them and go home if I can't stand it. The problem with 90 here is that it is most often accompanied by high humidity and bad air quality. Since I have asthma, I won't risk it. Yesterday, I did an almost 40 mile ride in 84 degrees almost 90% humidity. It truly sucked, but I did it. The only reason I will go Wednesday is so far, there's no bad air alerts.
I find my best riding temperature is between 55 and 65.