I have the GM and it is fabulous. It looked too large at first, so I went back to the boutique intending the get the GM, but decided to stay with the GM and am so happy!
I like the size of the PM. It's roughly the same size as my Mahina L. I've never tried on the GM but I've seen it in person and it is huge. My friend has it and she's 5'9" and it still looks pretty big on her.
I saw a lady at the airport,she's about 5'1 like me and also slim and she had the GM...the bag seems well used and has the smooshy look...it looked great on her.
I had the Galliera pm for a few months and it felt like it wasn't wide enough. I got rid of it and got the gm. I love it! I ended up getting the gm in a azur to. I agree the gm has more wow. I also have the Palermo gm to and love it. I also stared out with pm in that one to and then got the gm size. Good luck