I ride my gravel bike at an avg of 12.7 mph that include paved sections, gravel climbs and descents. At times I may be huffing along at 16 mph on a flat part of the route at time 25 mph going downhill. Even at only a 12.7 avg I feel like I’m getting a good all around workout due to the various terrain. Riding with 700X40 essentially MTB tires slow things down somewhat but my objective is endurance and general fitness.