I was thinking of getting the Speedy 35. Then I saw a pic of a girl carrying a 40 and loved it! THEN I saw a pic of a used Speedy [nice and "stretched" out] I guess you could say and loved that! Well my question is after you use your 35 for a few months does it expand or loosen up ? Or should I just go for the 40? TIA! [I'm 5'11 and weigh about 170ish, which one would suit me better? ]