pleeeassse anyone? or at least: how tall are you annalcg and PsychoBagLady? I'm considering a St. Louis PM vs a Fidji. I prefer that the Fidji closes with a zipper, but I have the feeling the St. Louis will fit more. Any of both more prone to sliding off your shoulders?
I'm 4'11", so pretty tiny. The Fidji is like a large hobo for me, and the St. Louis PM fits me as a large tote. The St. Louis absolutely fits more, but, as per your concern, it does tend to (try to) slide off my shoulder especially when I'm wearing a thick coat. If I don't have much in it, sliding is not a problem. On the other hand, the Fidji barely slides; I've only encountered this when I've stuffed it so it's quite round (usually with clothes; I don't do this often, don't fret!).
As for your question about A4 notebooks, I'm not sure of their size...If I'm not mistaken, they're longer and narrower than American notebooks. I have a few Clairefontaine notebooks that are longer and narrower than an American spiral notebook, and they fit. I hope this helps, sw0pp!