I'm about 5'1", 105 lbs. I use a speedy 40 all the time, it's like a tote, I guess I just like the look of BIG bags (also have the Manhattan GM). =)
It's really a matter of personal preference, OP! I always carry papers and such, so the 40 works for me. I find the 25 and 30 far too small,but the 35 would have been fine too.