My wife travels the Winter Garden to FWB route a few times a year to visit her mother; we both used to live there too. The fact is that the fastest route is definitely Turnpike to I-75 and then west on I-10. You just can't beat expressway driving on the other routes. She just drove it this past Friday and it took her 6 hours of driving time plus about 15-minutes for gasoline/snacks. By the way, Tallahassee/Leon County has expensive gasoline prices and she fills up just west of Tallahassee where US90 crosses over I-10. There are large truck stop/gas stations on either side of the interstate there.
The alternate I've used (for variety, not time-savings) would be from Ocala to take US27/US27A northwest over to US19 at Chiefland and then north to Perry. At Perry you go west on US98 until you meet SR267, you use that to connect to SR20 and then head west on SR20 to Niceville. The road is well-maintained and especially straight west of Tallahassee but the speed limit is much lower, a slow vehicle in front of you can back you up and if you're over the speed limit, you 've got to worry about the FHP.
BobK/Orlando