General Slant and Gas/Octane ???

Any other variables like where you buy your fuel. Not all gasoline is the same regardless of octane rating. Here's some propaganda about fuel quality

http://www.toptiergas.com/why.html

If you buy your gas at a small time no brand station you never know what you are going to get. I like to stick with the big stations like mobil, bp, 76, shell. At least you know who refines their fuel for them.