I have to agree with @Poet, The best runner in the our tri club, Daniel Gartner, runs a sub 2:40 marathon and 1h10m Half. At the Helveticman Tri, I passed him on the bike about half way round, and he then kept up with me, I came out of T2 around 4 mins ahead of him, and expected to be passed in the first 2 km. He never passed me, in fact his run was 20 mins slower.
For a good AG, the key is not to be an amazing running, but be a good cyclist who can complete the bike leg with plenty of reserves to run. Looking at past results in Lanza, people seem to leave it all on the bike course and then have a terrible run.
I’ve not got a specific program, but early on the season, I was running a half marathon every week, usually at a slow pace and often fasted. The aim was always to do a negative split. The fasted runs (I would say at least once per month) were incredibly painful
I also often do fasted long bikes, then a brick.
What I have found is that I always have a really painful period from the 2nd to 3rd hour, after the 3rd hour I am good for a long time, but at a lower intensity. For example, on the bike I can ride at 270w for 2 hours, then I will struggle to maintain 200w for an hour, then I am good for 230w for a long while. I think that this is the period where I go from using glycogen as primary energy to using fat.
What this means in practical terms is that all of my triathlon runs are in this fat burning state. And I need to train to maximise my run pace at this point. So riding 5 hours is 3 hours getting your body to the right point and 2 hours training. Alternatively you could ride 3 hours and run for 1 or 2 hours. The issue with that is running knackered is much more likely to result in injury
I’m now waiting for the coaches to shoot me down