It seems a shame to close in this porch if you are not heating or cooling it in such a hot and humid place as Florida.
- I'm not sure this would work, but what if you installed a misting system to settle the dust instead of trying to keep it out?
- Or, if the climate is too humid for that, what about blowers that are at the house side so it blows dust away and also cools the people in the room?
I know I'm not answering your question about these glazing materials with suggestions, but a sunroom is usually on the south side of the house, and I don't want you to roast.
Of the choices you mentioned, however, I would go with a low-E glass. The technology is evolving all the time and you can get a very efficient system these days.
I would be sure to allow plenty of ventilation.