That is definitely impressive stamina. An Olympic marathoner can average 12mph for around 2 hours and an "average" marathoner does 8mph, but that is on a road or track. Savannah is one of the few terrains where you could approach those speeds. I would believe they could go 50 miles on a hunt. Trying to run far in sand or snow, through heavy vegetation, or up and down mountains drastically increases the energy it takes (and the max distance and speed you are capable of). That's a whole other thing.