Vito,
I have experience with Adriatic Moto Tours (Italia Capuccino 9 day tour of Tuscany) and Ayres Adventures (Brazil.)
Both tour companies are excellent, with very good, knowledgable guides and very nice accommodations.
I'm 5'8" with a short, 30-in. inseam. On the Adriatic Tour two years ago, they had a single Suzuki 650 V-Strom available, which I wanted, but my buddy booked it ahead of me. (We were both riding solo.). I got a BMW F700GS, and it was fine.
On the Ayres Adventures tour, I got the then standard bike, a BMW F650 GS. It too was fine for solo riding.
The Adriatic Moto Tour in Tuscany was a RIDING holiday. We rode the twisties every day, with sightseeing stops typically short, and the guid urging us to move on to the next scheduled stop for coffee, lunch, or another tour site. And when we were back on the road, it was usually twisting, mountain roads, with the guide leading at a fairly rapid pace. This was NOT a relaxing, easy paced tour. It was go, go, go.
Also, in Italy (Florence, where the Adriatic Moto Tour started and ended), traffic is abysmal.) If you've driven in Rome or Paris, that's what Florence is like. Lane markings mean nothing. If there's space, cars, trucks, motorcycles and bicycles WILL occupy that space. You need to ride aggressively to merge, but drivers are used to motorcyclists and they will give way to you eventually.
Our group on the Adriatic Moto Tour were all seasoned riders with decades of Canadian and American riding experience, but we were all astonished (and not in a good way) about how fast the Italian motorcyclists blitzed past us on the secondary roads. They regularly passed us on the outside of curves, and honestly, we all found it unnerving.
The advantages of having a guided tour are many:
-language is not a problem; our excellent Slovenian guide spoke Italian fluently
-lodging and food stops are not a problem, because the guide leads you directly to these, so there's no guessing where to stop
-fuel stops are planned, and the guide records each rider's fuel bill at each stop and he pays for everybody at that stop, saving time
-each rider pays the guide a sum, say 20 Euros, which goes into a kitty, so he can pay the bill at coffee stops, until the kitty runs out, then each rider throws another 20 Euros into the kitty until it runs out
-eahc bike is fitted with gps and the tour's route is programmed into it; riders can choose to leave the group and ride independently, then meet up with the group in the evening at the scheduled lodging stop
-you get to see some unique, special places you might not otherwise find on your own
The disadvantages of the guided tour are:
-you don't get to see what you want to see
-you are constantly being urged to move on to the next destination to maintain the schedule
-the riding pace was very quick in our tour, and we had to ride fast to keep up with the guide
-even though the number of miles/kilometres we travelled per day was not particularly high (compared to touring in North America), the days were long and tiring because the vast majority of roads were tight, twistiing mountain roads, and being a flatlander, not used to riding tight roads for literally hours on end
Some final advice. Choose your tour wisely. Do you want to RIDE? Or do you want to sightsee on a motorcycle?
If you're riding solo, a 650-700cc bike will be just fine. Most of the roads on our Italian tour were secondary highways, so you don't need a large displacement bike. Even on the autostrada, the guide doesn't lead at a high speed, because he needs to keep the group together.
Riding in Italy is VERY different than riding in the U.S. or Canada. Motorcycle riders and car drivers travel VERY fast and although (car drivers especially) are highly aware of motorcyclists and give you room to pass. But riding there is much more stressful than riding here, just because of the sheer volume and density of traffic, and Italians' much more 'cavalier' interpretation of road regulations.
Tim