Yes Polaris backspeced everything to 50 grade, but either way I'd use an HDEO. Most of which are 40 grade, which will be fine if you're not the kind of guy that runs the absolute snot out of your 4 wheeler. Don't worry about the XW- number so much especially as you're in Florida.
My personal choice would be 5W-40 Rotella T6 Full Syn.