You can get give any advice on fuel economy, getting 26/32 is bonkers low.
Also, ten hours alone is not dangerous; just need ways to keep yourself focused. Also 6 hours to 10 hours would be a 67% increase, speed limits going from 65 to 55 would not change that.
BTW, google maps claims its only a four hour drive anyway.
You lose a good amount of mpg when you drive an automatic 4 speed instead of a 5 speed manual that's for sure. I actually log my mps, those are real figures not exaggerated.
It would be a 70 to 55mph change for around 100 miles of the trip. No matter what route you take from Florida to Atlanta you will always be driving through construction, interstate traffic, and Atlanta traffic. On any given day you can be stuck in Atlanta traffic from 30 minutes to a hour and a half. But enough of that I know how long it takes to drive to my own home smartass.
You say driving long distances isn't dangerous if you keep yourself focused? I say the same to driving fast, that's an opinion. I can also say I've gotten very close to an accident from driving long distances when fatigued while speed has never put me anywhere near getting into a collision.
You know what else is dangerous? Switching lanes while not keeping up with the flow of traffic, merging onto the highway below highway speeds, and pretty much any moving vehicle/person/object on the road going well below the speed limit.