I dive Boynton Beach with occasional trips up to Jupiter year round. I have a 3, 5 and 7mm full wetsuit and a 5/3 mm hooded vest. I wear them all during each season depending on water temp. I have the hooded vest (by the way, as opposed to DD, I wear it on the inside) on every trip in addition to the wetsuit chosen. In addition to seasonal water temp variation, we get cold uprisings and significant thermoclines. I was diving in Jupiter the 3rd week of September on the wreck trek during Goliath Grouper aggregation and there was a sharp thermocline at about 50 feet with a bottom temp of 67 degrees. Unfortunately, it was 82 degrees the day before and the cold water was a surprise. I was very cold in my 3mm and hooded vest, but not as cold as the folks in less, and there were many.
I have a really warm hooded, fleece lined boat coat made by TruWest that I take out on every boat trip from fall through spring. Be flexible, stay warm.