I live in St. Pete. I am training for a 1/2 marathon so not doing much biking so I am not doing this (but would love to do this ride). I know of the Horse Farm 100...not done it but heard. It is hilly, so it is tough. My understanding is that if you really want to see the good country go for 100. That being said...I am a slow rider. And at my best only avg. 15 mph. I am a "descent" hill climber. But this would be a very difficult course to do w/ minimal training. I can "crank out" a slow century w/ minimal training...just lots of experience w/ endurance. But I would not try to do a hilly 100 ride. Flordia is flat, but this area is known for some good hills and those that are really deceiving--dont' look all that bad but you find out 1/2 way up you are in the wrong darn gear!
Go w/ your gut---not your desire. Test the shorter routes to give you a better indication of what to train for next year!
Even the shorter routes should have some nice country and farms to see.
K