I owned a K4 3600 and an Ark with Stryker bag for awhile to compare. (5-8, 44” chest). I did hunt last year with the K4 and had hunted previous years with a Kifaru duplex amongst other packs. After quite a few miles and back-to-back comparisons I kept the Ark/Stryker. First off, both are very well built and have excellent customer service. Two things differentiated them to me: 1) the Ark slides down less, and 2) I prefer the Stryker bag system.
The K4 would slide down to where it felt weird on my butt and I would have to stop, lift pack up and cinch it down again. Or, let some of the weight ride on the shoulder straps. With the Ark I rarely need to adjust and can leave the shoulder straps pretty loose.
The K4 bag has a lot of straps and getting anything out from other than the lid I find to be a minor annoyance. In their latest podcast, EXO discussed how they used dry bags to make switching packloads easier. That is what the Stryker does so well. Put all of camp in a dry bag on the “load shelf” and day hunt gear in the Stryker bag.
The K4 hip belt pockets are quite good. I am using one on my Ark. I much prefer the Kifaru rifle carrier while hunting, though the K4 works great for hiking. I could never get it smooth and easy to release the rifle on my K4 and couldn’t use it while hunting. You could use a Kifaru gun bearer on the K4 for hunting.
How you like organize your gear could make one or the other stand out for you. You really do need to try them when it comes to fit.