How hot is too hot?

We are torn between having our reception inside or outside (our venue allows both, ceremony is outside). I love the look of the outside reception, however I'm worried being outside for an extended period of time in Florida in October will be too hot. The average high in October in our area is about 85. We are thinking of a 3:00 pm ceremony, which would put guests outside in the sun for about 4 hours. The cocktail hour will be held inside, and there will be plenty of room for guests to take refuge in the A/C, I just don't want our guests to be miserable during the ceremony and reception. So, how hot is too hot? Does this scenario sound unreasonable?