I have packed out a lot of elk solo, but never that far. I've been able to get a bull out in 3 trips a couple times, but that was boned out smaller bulls. I also had a big bull that was 5 heavy loads boned out. I think to pack a bull out that far solo, you will have to get lucky with the weather to not lose meat. In warm weather, you are not going to be able to get it all packed out before spoilage sets in. Packing 80-100+ lbs 6-1/2 miles one time is hard, but not really a big deal. Making 4 or 5 heavy trips for that distance over the course of several days and not hitting a physical wall will be an enormous task.