Others' experience can help you bound the risk but compare your apple to someone else's, not to their orange. The more detail, the better you can judge.
IMO, once you exceed factory stress levels and usage models (load, rpm, time) you are rolling the dice.
I expect Pontiac engineers kept the max stress below the fatigue (endurance) limit of the material, effectively eliminating risk for fatigue failure. They could even have had the luxury of adding a safety factor.
But once you push the stress above that endurance limit by raising the HP, modifying the piston/rod weights, or exceeding the max rated rpm, the crank will eventually fail. Like HIS shared, how long it takes depends on cumulative history of time and stress levels (Goodman diagram).
So when you share your broken crank experience, the more detail about the application and use history, the better others can compare.
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