You could go with 91 because it the better gas to run at average boost levels. The octane of the 94 sunoco gas is made up with mostly ethanol.
If you’re not pinging with your 91 you’re wasting money and making it harder to ignite your fuel with 94.
Higher octane does not always equal to more power or better. Use the octane that your setup requires. It’ll make more power and it’ll be cheaper.
Okay, mileage. I get about the same with KA or SR or RB20. If I’m boosting hard all day, its pretty obvious you’ll kill your gas tank faster. Good mix of both and I get the same.