I use Sunoco super premium in my Da 50R, I think the octane is around 93 and it is advertised as not having ethanol additives. Internal combustion engineers will tell you that octane rating only matters when cylinder bore is larger than 2.5 inches when pre-ignition becomes a problem with engines that have compression ratios higher than 9 to 1. Most engines built today are less than 9 to 1 compression ratio. The single biggest performance factor model engines are concerned with is the ethanol mix. Manufacturers say that there are no negative issues with ethanol gas but my many years of repairing motorcycles, cars, and trucks working for dealerships proved to me that there are some expensive fuel system problems caused by ethanol. Even the Walbro carbs we get with our gas engines are fitted with ethanol "resistant" seals and gaskets. Unfortunately the corrosive effects of ethanol fuel can destroy the metal body castings if any gas is left in the fuel system after flying,
There is a reason that ethanol is not transported by pipeline and is mixed with gasoline at the distributor level- it destroys almost everything it comes in contact with. If you run your motor dry after flying sessions you won't have any problems. When gasohol absorbs moisture in the air it forms acid compounds.
At the time when all the local gas stations were switching to gasohol I began buying Coleman camp stove fuel. It is expensive by the gallon but there are no engine problems caused by its use in model engines, only a distinctive smell. Colman fuel is around 50-60 octane. When the Sunoco ethanol-free gas became available I switched to it and a lot of my friends are full scale pilots so they get their gas from the local airport. Airport fuel is 100LL and they don't have problems with it either.
If you buy midgrade or premium from gas stations it has ethanol mix in it unless labeled otherwise. I don't believe you will have fuel problems with any type of fuel in your model engines as long as you run it dry after flying sessions. I have found that the fuel tubing the hobby industry supplies is affected and will get hard after 5-6 weeks when exposed to gasohol-even TYGON tubing.
There is a type of tubing that is black in color that is claimed to be unaffected by gasohol but the only time I got any was when a hobby supplier gave 3 feet of it to every entrant at a local event.
A lot of overheating problems are cause by incorrectly set ignition timing(both retarded and over advanced). You can make an overheating engine cool down by going rich on the carb fuel needles. The most important fact is to have 3-4 times more cooling exhaust than intake area.
I don't have cooling problems with my model engine setups and I have never used spoilers on any of my planes. The guys who fly with me will tell you that I run my motors hard and use large high pitch props on gas and electric. Field temperatures here in Florida get to 100 degrees.