Fuel octane

I strongly disagree. Even the cheapest gas today has all kinds of additives including plenty of detergents. I have not heard of sticking valves for a couple of decades, but that is an issue with coked oil, (sludge), not a fuel problem.

The bigger concern is the octane rating. Way too many people incorrectly think the higher octane means more power, but that is not true. Raising the octane allows engine designers to design an engine that is capable of developing more power, that is all that is done by raising the compression ratio, and that leads to pre-ignition; the same thing that we need to light off a diesel fuel mixture. You would hear pre-ignition as spark knock. Additives are used to prevent that, and the amount and type of additives go into the octane rating.

To say that a different way, the higher the octane rating, the harder it is to get the fuel to start burning. You could go overboard and use 100-plus octane aviation gas, but your engine would not even start or run on that. It is the same gasoline as 87 octane, just with more additives to prevent spark knock.

What is more likely to happen with the higher octane fuel is you will get occasional misfires under just the right conditions. The minor consequences of that are slightly-reduced fuel mileage and slightly more emissions. The bigger concern is that unburned fuel and air burns in the catalytic converter. If that becomes bad enough, the converter can overheat and the catalyst will melt and become plugged.

Your goal should be to use the lowest octane gas you can get away with. Be aware too that most gas today has ethanol in it. Ethanol is very corrosive which makes it great for cleaning. You will get much better fuel mileage running non-ethanol gas, but the ethanol will keep the engine cleaner.

The only times I have seen 4Ls with carbon build up was due to the PCV system being faulty. Higher octane will not solve that. It could actually make it worse.