What kind of gas is everyone running in their 2012 Si's? The gas cap states "Premium Unleaded Recommended". I feel like I should only run premium but several friends that own or have owned premium gas drinking vehicles (Mercedes, Porsche, BMW...) have told me that they often run a tank of premium then a tank of mid, alternating back and forth due to the price issues. Dad asked me why I would buy a car that only takes premium and suggested I fill it up with regular every now and then...I did this once and my gas mileage went down the crapper! Seriously, mileage on a tank of regular was around 20mpg. The car did not run any different so to speak, no knocking or valve tapping noises, acceleration still seemed solid and quick. But, the fact that my mpg was so bad, it made it to where I have not wanted to run anything but premium since. I quickly poured some Octane booster in and topped off with 93 octane after realizing my mpg's were so bad (about 120miles after fillup). So, what are you guys and gals running, 93 octane only? What about in states where 91 octane is the highest you can get (some parts of Arkansas and Missouri only offer 91)?