In reply to Flyinggardener:
I would always try on, as I often go large/r, as when taking the slack on the waist belt the gear loops are further forward (I prefer), if you go small and are the extreme end of being almost too big for the fit, then the gears loops are way back and there isn't enough slack in the waist belt to undo it a little and step out of it, you have to rethread the waist belt every time.
You also have to consider if it's for winter too, allowing space for a few layers of clothing etc..
Post edited at 19:35