In my experience, elk especially bulls are big and heavy. Here is my experience from last year with two average+ bulls.
The first was packed out with three guys in one trip. This was all moderate downhill through a long rocky slope without a trail. This elk was quartered and bone in with all neck, brisket, rib meat, etc... Full head, rack and 2/3 the cape also went.
The second bull was a little bigger and was boned, with all neck, brisket, rib meat etc... Head minus lower jaw, rack and 2/3 cape was packed out also. The second bull was packed out in two trips by two of us. This pack out had moderate up and sustained down hill with a lot of bushwhacking, no trail again.
Neither of these pack outs were longer than a few miles one way to get to a road. In either case it wouldn't have been possible to pack them out in one trip with just two guys.