With all due respect, I wonder if perhaps you may disallowing that aspect a bit too quickly, about plug color or electrode disintegration and fuel mix ratios. Unless i was getting erroneous information, my readings inform that oil mix also effects the fuel to air ratio, because greater or lesser amounts of oil also changes the amount of gas coming through the jet(s). More oil means less gas, and a leaner mixture going into the cylinder, at least to a certain extent. It occurs that although you may be getting better friction protection with the increased oil, you might also be getting hotter temperatures at combustion. You see the topic of mix ratios and jetting being discussed at bike and flight forums, but I can't say that I have seen it much discussed regarding chainsaws. Would there be something different going on? Confusingly interesting.....