Longbow:
I love REI. But, couldn't use them for a pack. Nothing they offered really did it for me. On-line is really tough, too, because you can't try it on. Kifaru is good because they offer a money back, no questions asked 30 day deal. Even better, I absolutely believe that if something like a Siwash doesn't fit right for whatever reason, they will make it fit. There's adjustment everywhere and they can modify the frame. Downside is, it takes about 6 weeks to get the pack in the first place and if you need to go back and forth, it'll chew up time and shipping costs. 2 others to look at. Arcteryx is good stuff and a lot of people like them. Mystery Ranch (Dana Gleason) is a legend and they will definitely make you happy. My strong suggestion is to forget REI when it comes to packs and call Mystery Ranch for starters and just talk with the person for a while 100% up front about all your concerns. You could do the same with Kifaru and could even talk with Patrick Smith. He's a nice guy. And don't buy anything. Let it sit overnight and if you're still hot on it the next day, order one. Worst case scenario is you'll learn a few things about packs.
Pete