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There is a lot of good information being exchanged on this board, and I welcome everyone and am glad to benefit from your views.
I think that the best arguments for LOP operation are (1) fuel economy and (2) the capability of running continuously at higher power settings.
I think everybody gets the "fuel economy" bit.
Assuming that the engine manufacturers knew what they were doing (and I believe the engineers did, since their charts are accurate), they determined that these engines could run continuously at 75% power using "best power" settings. If I understand correctly, best power is somewhere in the range of 50 to 100 degrees rich of peak egt, and is very close to peak CHT (CHT is pretty flat to the rich side of peak cht anyway, dropping only slightly at full rich). So, by definition, any change in mixture from this setting will result in (1) somewhat less power, and (2) somewhat lower (or the same) cht's. In this sense, using these settings is "idiot proof" (assuming you set the MP and RPM according to the book). In other words, it would be impossible to exceed 75% power, or to make the engine run hotter, by playing with the mixture control.
Of course, what the manufacturers were really doing is establishing a "design point" for continuous cylinder temperatures. I don't think that there is any argument regarding the fact that cylinder pressures are much higher at max power than they are at 75% power, no matter how you achieve 75% power? So at cruise power settings, we are mainly interested in limiting temperatures.
What LOP operations permit you to do is to maintain comparable CHT's and pressures relative to this "design point," while operating at higher power settings (perhaps 85% or so). Or, alternately, you can operate at the same 75% power LOP (at higher manifold pressure), and have cooler CHT's.
This second scenario is where some LOP advocates try to make the case that cooler CHT's translate into longer engine life. This is the part of the argument that I am having a hard time buying. I think we could all agree that 380 degrees is much better than 480 degrees. But that's not what is at question. If you are already running at 380, is 370, or 360 really any better? I kind of doubt that it makes any meaningful difference.
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