They are not aggressive at all. Just drive the way you would normally. If you are a slow driver they'll simply pass you whenever they have a chance.
I have a house near Poppi. The area is mostly rural, although agriculture is not the main industry anymore. Wood mills, textile, furniture manufacturing, and production of commercial pre-fabricated warehousing are the main manufacturing industries, along with tourism (especially nature oriented due to the presence of probably the largest national forest park).
To get there from the airport you have to drive through Florence, go to the SS67 via aretina toward Pontassieve, which is east of Florence along the river Arno, then after Pontassieve, turn left to the Consuma Pass (SR70).
The SR70 is a steep road going up to Consuma then down to the Casentino valley. It's a very curvy and not too wide two lane highway, so drive carefully. Occasionally you find the slow truck along the way. Overtaking vehicles on that road requires aggressiveness and high skills. If you don't have either, don't try it. Just be the slow car being passed by the local aggressive drivers (like me), rather than the other way around. It's a beautiful drive in the middle of forests (and wineries at the lower altitudes on the way up).
There are a few spots in Consuma where you should stop for a focaccia (that's their specialty). One is in the town itself in the little piazzetta and go to one of the forni (Forno=bakery). a little further up, (not even 1/2 km past the town) at the very summit, there is a wood hut with a large parking lot on the right. It's exactly on the summit. Best Focaccia and pizza ever, with porcini or whatever. Shortly after Pontassieve, before the croassroads to Pelago, there is a wine bar called 'Il Quartino' in the middle of the Frescobaldi wineries. You can stop there too if you want, to buy and taste some good wine. However the focaccia at the Consuma pass is a must.
From the Consuma pass summit down to Poppi is less than 30 min. Once again lots of curves.