I dont usually get on forums very much but I decided to get on tonight and saw your post. I cant comment on how kifaru does with heavy loads but I can comment on how my Brooks pack did with some heavy loads. I packed my bull and my weeks worth of gear out in 2 loads from 5.1 miles back in a completely roadless area. In some ways the pack did good, and in some ways it didnt. The frame, internal meatshelf, and loadlifters were great. The weak part of the pack is definatly the waistbelt. The belt kept on slipping off my butt and putting the weight on my shoulders making me constantly have to readjust. I couldnt get the belt tight enough to stop slipping off my butt and allow the weight to be on my hips instead of my shoulders. Packing a big bull and a weeks worth of gear out in 2 trips is alot more weight than most people carry and while the material used for the pack is durable enough to handle that kind of weight, I honestly dont think it was specifically designed to carry that much weight comfortabley. If they had a waist belt that was wider, stiffer foam, a legitimate lumbar pad, grippy material on the lumbar pad, and forward pull tensioners, it would be alot better!
I also shot and packed out 2 whitetails during the 2018 season. Both whitetails were a couple miles back in the back country. I quartered up and packed each whitetail out in 1 load. For packing out a whole whitetail the pack did great. No real complaints. I have found that up to 80lbs the seekoutside packs do great. From 80-100lbs they are just ok. Once you get around the 120lb mark and heavier the waistbelt sucks and causes some serious issues. If you are not planning on carrying more than 80-ish lbs, I think the seek outside packs are a great choice and that you will be happy with them.
I am keeping my Brooks pack, but I will be buying another brand of pack this year to test out in 2019 to see how it does with elk loads.
The 3rd picture is with my days worth of gear and a quartered up whitetail in the pack.