For what it's worth, I bought this one.....
Tamrac 5585 Expedition 5x Backpack (Black) 5585-01 B&H Photo
.....exactly 2 years ago - in anticipation of our family vacation to the Grand Canyon and other AZ locations that summer. It worked (and continues to work) like a charm. It held a K20D and K10D (both with lenses attached for quick shooting), 3 additional lenses and had plenty of extra room for a rocket blower, spare battery and charger, extra cards, a few filters, etc. I used the laptop slot in the front for paperwork - like boarding passes, maps, etc, and the tripod holder even allowed me to bring my small travel tripod.
It's a great case to hold all my gear for storage at home, and I've used it many times since to haul gear to kids sporting events, on vacations in the car, etc. It's very stable when you snap the waist strap on, and pretty comfortable for lugging around all day.
My 2 cents.....
Tim