If they weren't raping us so badly for gas I would say the slight premium on 91 (vs mixing) would be fine to cover the bit of extra wear and tear on the pumps toggling more to mix the gas.
But they're assholes so fuck'em
Originally Posted by HKS PWR
You did not account for the ethanol in the 87 octane gasoline, which is blended with ethanol (has a lower calorific value/energy content). Overall, you've blended gas that is "lower quality" than straight 94 octane gas.
Mixing is how the pump gives you 89 and 91 anyways, that's why it says "may contain up to 10%". If the 87 is 10% and the 94 has none, the 89 and 91 will be less than 10% ethanol.