if you are looking for a frame pack I highly recomend the gossamergear Mariposa Ultralight Backpack. it has 4200+ cubic inch capacity, large side and front pockets, carbon fiber frame, padded shoulder and waist belt, Y lash strap, shock cord compression, and all for just 16oz. now you are coming from a very durable pack so it will be different from what you are used to, but dont worry, because I know someone that swiched from a Lowe Alpine Countour IV(6400cu. 6lbs empty) with no problems. But if you are concerned about duribility, you can email Glen from Gossamer and you can probably get a custom pack made from a more durable material

http://www.gossamergear.com/cgi-bin/gossamergear/Mariposa-Standard.html