Hi Veggie Prof,
I live on the gulf coast of Texas across the street from NASA Our weather is quite similar to Florida. Very rarely we will have a winter night that goes down to freezing but it does happen. Our Birds froze to the ground when that happened 4 years ago. They have grown back to about 8 feet since then & they have sent out new pups.
They never exceeded about 12 feet and then they got knocked back by a freeze to keep their height in check.
I do not think you have to worry, if one grows too tall you can chop it back and the pups beside it will still give the privacy you need.
Otherwise You can consider growing fruit trees pruned as a hedge such as grumichama and Barbados cherry.
BTW, i just saw a blue and white bird of paradise at a local nursery 6 ft. tall for sale $200 so don't toss them, they are very popular and here are not easily located.
Happy Gardening !
P J, the Dirt Diva