I have the PM version, but yes, the GM is pretty big! Bigger than a Mezzo, but if you plan to carry books, then I think the Palermo GM would be great for you. I think someone did buy the GM..... here's the thread with a modeling pic:
When you buy your Palermo GM, ask to look at several of them (if available) and scrutinize the zipper - make sure it zips properly and to the end. I had to return my PM because the zipper was really wavy and didn't zip properly to the end of the zipper. But, I got another Palermo PM yesterday which was much better!!
The GM will be good if you are carrying books because if you put it down on the floor, you won't have to worry about a vachetta bottom - although there is vachetta piping on the bottom of the bag.
I still plan to cut out a piece of cardboard for my PM to make the bag a bit sturdier on the bottom of the purse.