I have a Gonex branded 45L pack that is very similar to this that I use for weekends in the summer. I stripped all the excess fabric dividers, cut out the zippers, then reinforced all the stress points to make it a top opening rube. I was able to get it down to 13oz, and have carried as much as 25 lbs in it while prepping for a more strenuous hike.

I can tell you that it's not comfortable with a load over 15lbs, but since it was cheap, I do not treat it gently. So far, it's been tough as hell.