I'm not sure if this has been discussed yet, but apparently the city of Miami passed a resolution that favors the secession of South Florida.
South Miami. Difference of about 407,845 people. That said, I'm in full support of this - anything that both makes the University of South Florida's name actually make sense (it'd be the flagship public university of the State of South Florida) and puts my education under the control of someone other than whoever the hell The Villages sends to the state legislature is alright with me.
Likewise, Pasco needs to stay with Hillsborough and Pinellas. Its not as if once you cross the county line you're in Alabama.
The counties I'm unsure where to place are Hernando, Lake and Volusia.
Pasco (and Hernando, as you mentioned) are in a gray area. I'd draw the line along the northern border of Pinellas and Hillsborough going along a pretty fuzzy line (that covers much of Pasco & Hernando). Most of Lake and southern Volusia would also be in that area. Volusia on the whole I'd say would go in North Florida, if only for the whole Dale Earnhardt NASCAR Daytona thing.
Indian River, Brevard, and Polk Counties are not South Florida. What a random map.
Polk is iffy, but Brevard probably goes in the new Southern Florida state we're making here - not exactly a place I'd expect to see boiled peanuts by the roadside. Brevard was largely grown and shaped by the space race of the 60s, after all. Indian River, meanwhile, is New New Jersey (in fairness, Fellsmere isn't, but the county's coast-dominated).
Orlando has more in common with North Florida than South Florida; that applies to pretty much everywhere in the state, to be fair. I'd just break apart everything in the Miami orbit, so everywhere that supports Miami over any other Florida team. That would mean West Palm Beach and down. No reason to stick Tampa and Orlando in a Miami-based state.
Just Broward, Dade, PB and maybe Monroe? Nah... Orange/Osceola is definitely not part of N. Florida. Though the North Orlando metro definitely is. Even East Orlando even feels like S. Florida. Its a looong story how I got to know the area. You could probably take in Tampa without having to take in Pasco, I think. There's NPR, but that's the only metro feeling place in Pasco.
Orlando is my blind spot; I admit don't know that area very well. However, I do know the Tampa suburbs, Clearwater and to a lesser degree St. Pete and they are MUCH more culturally similar to North Florida than South Florida. I know it doesn't make a very pretty map, but unless there's some measure I'm missing I don't see the justification for grouping Miami with pretty much anywhere else in the state but West Palm Beach.
Orlando, at this point, certainly isn't the south. Maybe a few decades ago, but not now. As for the Bay area, we are home to the largest rebel flag in the world, admittedly, but the area is a better example of a melting pot of both cultures than probably any other in Florida. I'd be hard-pressed to call the area Southern, especially St. Pete.
People need to understand that central Florida--the I-4 corridor and adjacent counties at least--are different from both north and south Florida. Culturally, demographically, and politically.
And of course this is the objectively correct answer.