Thanks guys. Unless I saw a few folks saying 'you definitely could fit all that comfortably in a 2200' I was leaning towards the 3600. Bigger is better, right? Or at least usually? My tripod does usually live with its feet in a side pouch and strapped to the side of the pack, but my rain gear definitely isn't the 'packable' sort so feels like 3600 will be a great fit.