Right then, an update.
Took myself up to Kit Monkey to try one on for size and look at alternatives. Tried a Karrimor Sabre 30 previous and didn't like. Anyroadup. Best advice is ring before you go, I didn't. However the gent was happy enough and luckily had one available. I'm 5'11" and under 17stone so wouldn't call myself too big (not all of me anyway). Fitted me fine (Munro that is) so have come away with one. Not overly generous in the shoulder but tried it over the bulkiest top I'm likely to wear under it and not going to be overloading it, brew kit, waterproofs etc only. Wouldn't have wanted it any smaller but has enough adjustment for me. No affiliation to Kit Monkey at all. Happy days....
Cheers.