Ok kids, today I tried a little experiment. I filled my 2013 Stelvio with E-0 premium in Amarillo for $3.75 per gallon. I could have bought E-10 premium for $3.35. I rode into Amarillo from the south with a strong southerly wind and the bike computer showed 52 mpg on E-10. I reset one of the trip computers after putting almost 8 gallons of E-0 in the tank and continued northward with a continued strong southerly wind. Stopping in Tribune KS for the evening my mileage on E-0 is exactly the same as was the E-10. The final 50 miles or so saw the tail wind abate so I'm willing to give the E-0 a 1 mpg advantage. That means under this very unscientific teats, E-10 is the more economical fuel.
Suck it, bitches.
In Russia we have saying, "if it isn't broke, don't fix it". We also say, "if it is broke, don't fix it".