What do you think of the speedy 40?

umm... what do you plan to use it for? cuz at first you say that you're a student, so I'm thinking that you're going to use the Speedy 40 as an everyday school bag which in this case, I do not think is a good idea. However, you then say that it'll be an overnight bag, so here the Speedy 40 would be suitable imo.
 
the 35 might be enough, I'm also a student. you have to roll some A4 stuff to get it in, but then it sits nicely in there. if you plan to carry thick A4 files then ok, you have to go with the 40, but otherwise the 35 is even enough as an overnighter unless you plan to change outfits 3 times a day ;)