I think if you are petite you can wear the larger size messenger, but you'd have to be very small. the smaller noe would look fine on your height, I used to have one and I'm almost the same height as you are.
You may have to buy another strap to use the Noe as a messenger style bag across your body. There's a mono adjustable strap that you can purchase separately. I was just looking at the Petit and to me that was plenty big to hold all of my accessory cases (about 4 or 5). I'm 5"3. I think the large Noe is nice but seems more like a tote bag - you can carry large notebooks, jackets, etc. in it. Another TPFer had a Noe with pictures showing how large the Noe was. Check the Noe club in the Clubhouse section.
I am 5'8" as well and have both, petit and regular noe. I can't wear either messenger style. LOVE them both so I am no help to you!:shame: I must say that petit noe fits quite a bit and feels great on my frame but so does the regular noe. I would advise you to try them on for size at the store to see which one you feel the most comfortable with.