Just ran across a quantification of "how much pack" in Chris Townsend's Backpacker's Handbook (4th edition.) He gives a rule of thumb that your pack shouldn't exceed 10% of your total load.

Applying that to me, it yields about 2 pounds of pack - pretty much what my old Granite Gear Vapor Trail weighed, and it handled 25 pound loads very well. (I let it go, finally, because my gear volume shrunk enough that it was too large and became floppy - and because one of the accompaniments of aging is a slight loss of torso length, which meant the fixed suspension no longer fit.)

FWIW, I'm not looking to change packs; the one I have now is comfortable and just the right size (even if it is a pound too heavy by the above formula.) I just thought this might make an interesting discussion.