The bags excel over long days. I personally test out all of our gear from the first concept to production models. The standard route I take them on is about 6-8 hours of rugged mountain travel.
The key for me is that even after a 3-5 hour tour I still have the mojo to actually snowboard down the run I'm heading to... and then hoof it back home. A good load carrying pack is pretty essential for days like this.
I took my Loka for a 7 hours jaunt two days ago. Here my turn around point.
I think they will do fine for books. As for the 13inch, I have a 13 and 17. 13 fits the sleeve. 17 fits but not in the sleeve. With ICU in place it holds it in a pretty good position, but I would advise a padded sleeve. My email is below if you have more questions.