I think in retrospect fat is where it's at...
Started at 10.1, then 11.7, then 12.7 on the dual O2 guage. Leaned one more jet size and still showed 12.7. Thought it was good (obviously!). I had 5" dual side exhaust pipes and they had a black haze, so thought it was still rich enough. Tiny black specs on a couple plugs, I now think was thermal coating vacating, still not sure. It was not aluminum.
I think if I would have lifted at the 5 mile it would have survived, but who knows. I know for this combo about 5 3/8 miles hurt it, and I stayed in it to the 6 because I made a bad choice.