I bought the REI Flash, took it home and loaded it. It was not comfortable so I took it back.

Last year I bought a GoLite Quest. I used it on the Sierra High Route (35 days). It comfortably carries 25-30 pounds, tolerably carries 30-35 pounds, and in a pinch (for a few days) I carried 40 pounds. I love the pack. It has a heavy-duty suspension for the total pack weight and a good capacity (11 days with bear cannister capacity). My only complaint is that it probably will not last too long due to my doing a lot of off-trail travel. It's durability is similar to the Granite Gear Virga. The shoulder strap padding is on the thin side - but you are not supposed to put a lot of weight on shoulders anyway.

Choose the pack based on fit. For me, the Quest was really comfortable from the get-go. For some odd reason, I cannot tolerate Gregory packs- my back is shaped wrong. No amount of weight savings is worth an ill fitting pack. And no amount of detailed product specs can substitute for trying out the pack with your gear inside.