For what it's worth:
The DC Randonneurs website has a page that says that less than 1% of all official RUSA 200km brevet finishers finish under 7 hours = which is 17.8mph or less.


I assume that the fast riders can go faster over shorter distances, but being human, woould eventually slow down.

So, over what distance are you figuring that people might be inflating their reported speeds or comparing your own speed to? It could be an apples and oranges thing - he's reported a half mile distance and you're thinking over 20 miles....

Other considerations, drafting or not, faired or not, recumbent or DF, flat terrain or hilly... and on and on.... Like I said, apples and oranges, maybe**********

Then again, your Ironman friend would be in the 1% of the RUSA finishers time-wise. Can you keep up with him riding an "equal" bike?