My experience with the reissue tells me that you cannot be sure on size until you actually TRY the bag on.
I'm 5,7 and went in the Chanel boutique already decided that I wanted the medium size. When I tried it on, it was fine. As I was looking myself in the mirror, the SA suggested I tried another size on. I started with the small size and WOW! It was much much better on me than the medium. I tried the large one on, and while this was fine too, I couldn't think of me using it much somehow. The reissue is a bag I would most definitely NOT carry at work. Although I work in an environment with a strict professional dress code (upper Government work) I just couldn't see myself with this bag in the office on a daily basis, it somehow looked "too heavy". So, the large one was ruled out.
Although it was the medium I wanted, I had eyes too, and the spectacle of me carrying the medium vs. me carrying the small was... no comparison really! All the salespeople in the Chanel boutique agreed.
I bought the small in the end, and I absolutely LOVE it! And although it doesn't fit many things (only the strictly essentials - money, keys, mobile, makeup, lipstick, card holder) it goes with anything, from a super leisure walk with gym clothes worn as a messenger bag, to a super dressed up night outfit.
Do TRY the bag on before you buy! You might be surprised!
(The Chanel boutique I bought mine from had only 3 sizes: small, medium, large - therefore I don't know the sizes in 225, 226, etc terms, sorry)