I put a lot of miles on a Granite Gear AC 60. They're a good pack, but they don't handle loads over 35 that well. Not that I do that often, but sometimes... I now carry an Atmos 50 and it does truly carry like a set of wings. I usually forget to use the sternum strap and have had zero discomfort. I need a pack to occasionally haul 6 qts. or more of water on our annual Grand Canyon trips and I usually carry the bulk of our gear and food. We also do a lot of winter trips and I sometimes am carrying fishing gear and a pack raft. If all else fails in your shopping, my Atmos makes carrying 20 lbs feel like 10 to me. The fact that it's heavy itself gets outweighed by its ability to perform. Best pack I've ever used for scrambling on Class 3 sections. It just may be the fact I have the fit dialed in, and my morphology is WAY different than yours. I'm 5'11 and 195. Still if you don't find something that fits your needs... Happy shopping!

Another note, I looked at the Lightening 45 and deemed it too small for my needs. Besides the fact I couldn't try it on in person , it lacked the outside stretch pockets I like to stuff my wet clothes and tent in. Style to me is function over form, so things strapped all over the pack that can shift or fall off speaks of afterthoughts and not well prepared. Kind of like throwing a Carharrt work coat over a Saville Row suit.
I couldn't find a pack called Buttermilks, but having lived in easy biking distance from bouldering there, I'll guess it's a climbing oriented pack. Could you provide a link for people like me, who lack research skills?