One this is FACT
All engines, large, medium and small are not alike. not even close.
Someone with an un-sensitive engine who goes around bragging "Ain't No Difference, You People Are Nuts. My Car Runs Perfect" sets himself up for ridicule. I am unlucky enough to own a Misubishi 3.0 engine. Feeding it is like trying to satisfy a six-year-old at the dinner table.
I had a friend in the states who simply sneered at my claims that cheap gasoline like Arco and Valero degraded the driveability of this engine. He drove it one day, it bucked and snorted, causing him to bite his lip. Instant silence and humility. It is not a question of octane - it may be a question (unproven) of the amount of sulfur present in the gasoline. Mexican PREMIUM is refined in the USA and is labeled UBA ultra bajo azufre, ultra low sulfer. Making the grade as a top tier gasoline, sans additives. In the winter they still add MTBE here.
Alcohol belongs in gasoline about as much as gasoline belongs in Kentucky bourbon.