Pardon my ignorant sKepticism, but why all this interest in a formula anyway?
IMHO there are so many different types of athletes out there... slow twitch, fast twitch,.... no twitch
....
If I pull a 1:41 and change split for 2k (6:45) and a 1:51 and change split for an hour (16k+) it may mean that I'm a better endurance athlete than a middle distance one
If both this times are my absolute bests the "double the distance, add 3 sec" would project a 1:53 split for the 60 min piece (or a 1:39 pace for the 2k => going the other way)
Of course it could mean a host of other things.
Formulae have a way of psyching ourselves out of improving too...
Hard work at a goal has a way of knocking away barriers by means of slowly progressing improvement.
In the end it all just seem like splitting hairs without purpose.
Other Comments: The longer distances and times are generally done w/o a partner or outside a race environment. For the competitive types like me that's a big difference from the push in contested 2k.
Secondly, just having completed a PB hour row, I feel my potential to improve at the longer stuff is higher.... Odd that I feel it will be harder for me to lower my Feb. PB at 2k
I also find yankeerunner's insight helpful (as a top runner of marathons) re: mental attitude (see "UK forum" topic today, elsewhere on this site)