I agree, the ratings are pretty subjective. If you look at a lot of the Gregory packs there is a volume difference between the different sizes of the same model pack, too. And what's more curious - my stuff expands and contracts to fit in whatever pack I have. A 60L gets full, then I put it in a 45L and it all fits with room to spare. I had a 50L pack that was a bit of a struggle to fit the bear can, but otherwise it was the same thing.

The packs I have found to be comfortable with 25-30 lbs are a Granite Gear Nimbus Ozone, a Gregory Jade, and a Gossamer Gear Mariposa Plus. Talk about a different fit between the stiff frames and the Gossamer Gear - the semi-frameless packs are neat but the packing strategy is somewhat different. But I often take the Mariposa Plus when not taking a bear canister. It drops the pack weight by two whole pounds.