My experience has been with mammoths (fossil)rather than elk. The heaviest was 95 pounds (actual weight on a scale), no trail, uphill, back to the truck, about one mile. I left very deep footprints.

Where permissible, I have used a two wheel game cart (an eight foot long tusk is a very awkward backpack). In my experience, they don't fit on a trail tread very well and continual use would tend to mess up the tread. A one wheel stretcher carrier fits the trail tread better, but the accompanying stretcher bearers will beat down the trail as they scramble around. I've done quite a few miles with those.

I did once carry a 165 lb victim on my back for about a quarter mile uphill (I was younger and full of adrenaline). It wasn't as hard as I thought it would be, probably because my load could center his weight on my body by draping his head and arms over my shoulders. You can't get that kind of cooperation from fossil mammoths or dead elk.