Back to the general topic of changing grades of fuel;
It's widely acknowledged to use the grade of fuel the automaker recommends.
One thing to consider is that not all brands of gas are equal. Simply changing company brands ( i.e Bp - Texaco ) may result in better performance and economy.
The quality of the fuel does vary between companies .
Where by the grade ( 87 , 90 , 92, etc. ) does nothing to qualify their quality.
Here are two sites to check out
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
http://www.faqs.org/faqs/autos/gasol.../preamble.html
