In reply to TNTTNT:
Hello
I bought my Osprey Kestrel 48 from Cotswold outdoor (multiple branches in the south east) the summer before last and they still had the Kestrel on display when was in there again at the weekend purchasing anther smaller Osprey bag, so they should be able to help you with the bags you are looking for.
Afraid I cannot comment much on which size would suit you best. It would simply be a case of finding a local store to you that has them in stock or can get them in from another branch and deciding which you'd prefer once you have seen and compared them both. What I can say is that the Osprey bags were for me at least the most comfortable to carry bags that I tried out when I was shopping around.
Good luck.