Retarding timing causes exhaust temps to go up since the engine isn't running upto maximum efficiency, there are videos on it, there was one when they took a bunch of cars (american, jap, euro, turbo and NA) and ran them with 91 and lower octanes. Most of them produced less horsepower and higher exhaust temps using lower octane.

Look at subaru ringland issues in the boxer turbo 4s, there are a few causes, one of them being low octane fuels blowing the engine.

Just saying modern cars are built for 93 octane and upto 15% ethanol, so no reason why you shouldn't be running to spec. These engines are running extremely high compression 12.5:1 in the 9A1 vs 10.8:1 in 993, so you want more stable fuel. You're also running over 100hp / l which no NA aircooled engine was capable of from the factory.

You're giving up more stable fuel in favor of no ethanol. Yet the car (watercooled) has been designed to take both ethanol and was optimized for higher octane fuel.

 

All who are worried about ethanol, race gas is available @ Mantis Racing , various grades, all ethanol free.94 octane and up, 5 gallon pails to 45 gallon barrels, or 20 L to 205 L. 905-84-6219