there was a market survey done at backpackinglight.com about ultralight gear haulers... but it's only available to people with a subscription over there. Several of the packs I have listed on my light weight packs would be worth a look. I would second people suggesting checking out ULA. When I was playing "sherpa" for the family, I found the Six Moon Designs StarLite / Traveler with stays works pretty well. If they Gorilla is working well for you and is just too small the Mariposa would be worth a look. I have no experience with it, but I have heard good things about the Elemental Horizons Aquilo and Mountain Laurel Designs Exodus.

As others have mentioned, there are real limits to how much weight you can carry in a frameless pack. Depending on the person, frameless is comfortable to 20lb +/- 5lb (I am in the no more than 15lb camp), minimalist "frame" - form or plastic frame sheets / very basic stays, etc 30lb +/- 5lb. Above that, you really want a pack with a well design frame and suspension system which in the best of cases is going to weight 3-4lb.

--Mark