Long distance cyclists tend to think about things in terms of distance over elapsed time which puts the OP just under 13.7 mph for a 72 ft/mile century with almost an hour off the bike. Most of the guys I ride with are in the 16-19 mph range for a century depending on hills and wind, with 5-10 minutes off the bike. These are just normal middle aged guys who would get dropped immediately in any cat 5 race. RAAM qualifying time for 72 ft./mile course is 360 miles in 24 hours or 15 mph. Christoph Strasser rode 3,020 miles at 16.4 mph when he set the RAAM record in 2014.