Well traffic will slow you down in a car (even a Ferrari!) so you could be looking at a longish trip.
Problem with doing a section of the road is that it is generally quite remote so if you do a part and then return it'll probably take just as long and then (presumably) you'll still have to get to Bologna on the A1.
Most of the SS65 is fairly distant from the A1 (with mountains and valleys between so limited access) however even the A1 has some good bends on it!.
Best idea is to start really early in the morning and miss most of the traffic - even better is to rent a bike to do it on there are companies in Florence where you can hire a Multistrada which is the perfect tool for the job (I understand the Ducati factory do rentals too) get one for a few days and do the Futa and as many other roads as you can fit in (time permitting of course).
Some great roads round Montaione though, in fact the whole area is full of great biking roads.
Buon viaggio.
