When I did the LDWA 100 in the Yorkshire Dales I averaged around 3.5mph.Fast walking pace by most people's standards but the only thing is I had to run at least half of it to keep up that pace.Just looked at the results 26 miles point 5hr 42 min,50 miles 12hr 5min,63 miles 16hr 34min(this part was in the dark),84 miles 23hr 55min,100 miles 30hrs 30 mins.
Average over fist 50 miles 4.2 mph.Most of this was run on the flat and downhill sections.
Average over last 50 miles 2.72 mph.I went through a very bad patch after 70 miles and only picked up again at the 90 mile point.
I wasn't carrying any kit other than a small backpack with the mandatory safety gear.This weighed no more than a couple of pounds.I finished in 32 place out of 500 starters.Not too bad for a first attempt but far worse than I had expected.Only three guys finished inside 24 hours Cudahy,Harney and Simpson.There were 233 finishers out of 500 starters.Most of them took over 35 hours.Theory is a fine thing but when you get in the field it all starts to fall apart.
I expect you will find that these guys are special forces, not the average bunch of recruits.
Might also be someone who does a desk job and has plenty of time to train.