I've been rucking 3-5 times a week, 4 miles a ruck, with 65 pounds alternating between my K4 and ARK since the ARK came out. I'll swap packs half way through, change the pack I start and end with, do a double lap with each, etc... and for me I prefer the ARK frame but K4 bags. I have a Dall bag I was going to use for my solo sheep trip on the ARK, but will be using this Absoroka on the ARK frame now instead. I wanted just a touch more access and this should be great for my purposes. I'll have my K4 7200 in the truck as a backup. Both feel good, but the ARK just seems to stay exactly how I started and never needs a synch or tweak throughout where the K4 I usually have to tighten or adjust something a tad. I'd give the K4 shoulder straps the nod, and the ARK lumbar the nod. Each back is shaped different so your choice may be the exact opposite!