The following statement is not to dissuade the OP--I hope she made her decision on which pack to use after putting all of her gear into both, and not on the opinions posted here.
That said, I often read people saying taking a larger pack denotes fear or insecurity, while I would say the opposite could just as easily be true: taking a smaller pack means the walker fears they will be unable to stop themselves from over packing. I think that is nonsense. People who cannot control over packing just tie things to the outside of their little pack, or cram things in and bust zippers, etc. I would say the vast majority of forum members are able to use a 40+L pack and not take extraneous garbage. This is especially true when the person posting is smaller, since both packs will actually be smaller than the listed 36 and 50L. Many have posted why a larger pack may be the more appropriate choice (build of the walker, how the weight is distributed in a larger vs smaller pack, etc). Many who propose smaller packs also walk in summer months, when heavy clothing and warm sleeping bags aren't required.
this is, in my opinion, another great forum fallacy: the size of your pack has nothing to do with how secure or insecure you are. The same could even be said about the weight, since you don't know why someone is carrying the size load they are--they may need medical equipment/supplies, they may not be able to afford the lightest sleeping bag, they may have special dietary needs.
Many of us can easily carry much more than the hallowed 10%. When people start shaving the bristles on their tooth brushes, and getting anxious about one pack weighing 2 oz. more than another, that says the effort might be better spent in training--and if physical conditions limit training, then researching pack transport.
