SightUpYes this is a very high quality brand! When I saw it on Massdrop I was hooked on buying it because at REI it was more expensive! I got the 65L Stout which fits me very well and I am around 5'10" so this should not be any problem but make sure you get the Stout and not one of the Amber backpacks because they are more for shorter people because of the straps and supports. And yes you can wash them they are the same material made for rain jackets and can be very durable.
Hope this helps!
SightUpStout is for male build, amber for female build, but you can always pick based on your physique and preferences. Size is dependent on your intended usage, doesn't make much sense to carry a 75L for a day trip when a 20L will do well. Washing can be done with mild soap according to instructions on gregory's site.
Also, I do not know this brand. Is it a high quality one? Can you wash them?
Hope this helps!