Just as important as the bag is the frame. You are going to be miserable hauling bulky,, heavy loads on steep, rough country with a frame that doesn't fit your particular body-torso and is capable of 100 lb loads. Most 5000 cu in frames aren't designed for these loads! I've been on quite a few sheep and mtn goat hunts the past few years and would definitely consider a larger bag.. As mentioned above you can always cinch a large bag but if you don't have room you are screwed with a small bag.
When I was searching I had packs narrowed down to Kifaru or Stone Glacier. I went with Kifaru because of all the rave reviews of the comfort of the belt, frame, and shoulder harness. SG didn't come in camo...which also was a deal breaker. The other thing I liked about Kifaru was it was possible to customize my bag with an assortment of lids, pockets, and assessories. The only thing I wish I could have changed was going with the longer frame for taller load lifters....which I can change. I have both GL2 and Timberline bags. This summer I used the smaller/lighter Timberline bag to scout and switched to the GL2 for my actual sheep hunt. It only takes me a matter of minutes to switch bags. I would also highly recommend a guide lid which is large enough for quick and easy access to raingear and other essentials.
I just packed out a bighorn ram yesterday. I could barely lift the boned out meat, life sized cape, skull/horns, spotting scope, tri[pod, rifle....althought it fit! My GL2 is likely around 7,000 cu in and there is no way I could fit this in my 5200 Timberline bag. I'm guessing all of these without my tent, sleeping bag, and gearq weighed 80+ lbs. Obviously if you are on a guided hunt your guide will split a chunk of this but I would highly recommend a large bag. There really isn't that much weight difference between 5,000 and 7000 bags and you'll love the extra room. If you spend a lot of time scouting it may be nice having a pair of bags!
