When I had my tuned WRX STI my experiences and mileage (no pun intended) varied drastically based on source/octane.
My preferences were;
-Petro Canada 94 (I REALLY miss this being an option!)
I ran US Chevron 92 countless times but never noticed a difference between this and Canadian 94 so I find it very interesting that so many people in this thread do.
Mileage was comparable and performance was nearly identical.
I HATED Husky 94. It was AWFUL....
Not only did I genuinely take a 15-20% hit in fuel economy (I did the math on this) but it felt like I had an extra 500lbs in the car with me based on power delivery, etc...
For the bike I prefer :
-Petro Canada 91
Long Live the King : RIP John (Gwilo)