Both are good and work you differently. Endurance rucks for distance at a good pace and intensity rucks with heavier weight for 3 sets of 10-15 minutes at a good pace. If you can do 60# for 4 miles in an hour on flat even hard surface ground and 80# for 3-15 minute sets @ 4 mph your doing good. If you also run and do full body strength training you will have more improvements,
Ray Jardine's Pacific Crest Trail Hikers Handbook might have want you are looking for. One of the 1st chapters is titled "The Pyramid of Hiking Style". It relates hiking with 8 days between resupplies. If you were to hike 17 miles a day at 2.75 miles per hour, you would hike for 6.2 hours per day. If we hike just 1.5 hours longer per day the daily mileage would increase to just over 21 miles per day. At 21 miles per day we would only need resupply every 6.5 day. We could then take out a corresponding amount of food and fuel and hike a little further every day still arriving in camp with equal fatigue. And so on…..Page 26 of Pacific Crest Trail Hikers Handbook. Hope this helps.