Rubber Side Down
Here's what it says on page 351 RE fuel ethanol/E85If you read the whole paragraph its talking about the fact that in some regions regular is 85 octane and that using premium will give better performance than 85. It does not say you will get better performance than 87 octane.
During the summer season, fuel ethanol may contain a maximum of 85%
denatured ethanol (Ed85) and 15% unleaded gasoline. The fuel ethanol
has a higher octane rating than unleaded regular or premium gasoline
and this allows the design of engines with greater efficiency and power.
This basically says higher octane = greater efficiency and power.