The science shows that running an engine at around 50 F degrees rich of peak results in the highest peak pressures and temperatures for the cylinders.
The science shows that the two biggest factors contributing to cylinder fatigue are pressure and temperature.
The science therefore shows that manufacturers who recommend that cruise EGT be set around 50 F degrees rich of peak were either ignorant or, as is more likely, trying to wring as much power as they could out of the engine in marketing competitions that used to be won on the basis of a couple of knots cruise TAS in a sidebar summary in the aviation magazine reviews of the latest model Cessna/Piper/Beechcraft etc.
The science therefore also shows that a person who considers POHs to contain immutable facts and the safest engine management procedures is the person with the religion problem.
(And science also shows why the deceleration felt through the seat of the pants is a reliable, repeatable and safe way of setting cruise mixture lean of peak on a confirming engine fitted with a CSU.)