I think the state will tell you that you have to carry it. Also i think it's only for DUI's and accidents not speeding..
Looking around on the net i was unable to find a clear answer, but her is what i found:

Florida's DMV is more like a room full of ostriches with thier heads in the sand. (not the best source of information and almost never right about iffy questions) If you havn't been told you need a sr-22 you should need one. Don't expect a correct answer from any one @ the DMV and if you are really serious about trying to find out if you need one, find an attorney that works in this area and ask him.