I have a 2006 base HiHy and use the cheapest gas available, never used anything over 87 octane. My mileage is a shown in my signature (click for details tank by tank). I do find that using the A/C fulll time dropped my MPG by about 2MPG. IMHO I would not use anyhting else other than regular. There have been several threads on using other than regular fuel. There never was a clear case where the extra cost fpr higher octane was justified.