Stepping up from 32mm to 40mm OBJ gets you 56% more lens area / light gathering ability, and if that little bit of weight hinders a person's hiking, they need to get into better shape.
Maybe so, but that does not necessarily equal a bigger exit pupil. Not to mention glass quality/coatings among other things is a huge factor in light gathering too. An individual's eye and their eyesight is also something to consider.
I (pun?) see (pun again?) Brad already mentioned the exit pupil and coatings thing.
