err Newcastle to London in 24 hours. Its only a double and a half bike ride and no running so should be easy peasy... just need to 'go easy' and let the miles tick by rather than pushing and blow up after 10 hrs.....
in IM Lanza I walked 100m, ran 400m, repeat, for a 4:37 or something (the joys of knee arthritis mean I can't do heavy training millage any more so I save myself for race day )
A personal worse by about an hour, but I was massively happy as my longest run was 5k.
I found I was fine for the first 2 laps, (20 k) then lap 3 was bad - could still run but it hurt Lap 4 was very hard. still 'running' but the missus could walk faster if she put her mind to it
however without conserving myself I would have gone south much earlier.
unless you know you can run well the whole way, the run walk makes massive sense. Plan to run between the aid stations, then walk a minute through it eating and drinking.
Most (80%??) will end up walking so plan for it, start your plan (what ever works for you) straight away and just keep plugging away. You will grind to a halt a lot later / will feel fresher than thos running the whole way... when they walk they really struggle to run again.