Blue, I do not understand your basis for saying "The higher the (octane) rating the cleaner the burn". I do not see any reason why this should be so. Octane rating measures resistance to detonation - if higher octane fuel burned cleaner in an engine that did not require that octane level, it would be by accident, simply because some of the octane improver additives and/or cracked or hydroformed hydrocarbons happened to have that characteristic inadvertently. From what I have read octane improvers, in particular, are more likely to make the burn less clean.
With regard to low octane fuels tending to increase fouling, that appears to have been true back in the days of very low grade petrol being raised to high octane by the use of large amounts of tetra ethyl lead, but those days are long gone. Large amounts of octane improvers may cause fouling, but it seems unlikely there will be larger amounts of octane improvers in low octane fuel, than in high octane fuel.
I generally agree with your warnings about ethanol, which tends to be unfriendly to fuel system polymers, and hygroscopic as well. The absorbed moisture causes fuel system corrosion, fuel discolouration, and ultimately may cause the fuel to become non-homogeneous.
