Take mine! That's the deal. I've read it numerous times on their website. The '05GTO doesn't have a better rating Bob(the '04 does). You knew that, but I had ta point'er out! The Mustang only "needs" 87 Octane. 91 is considered high octane in some places, and GM recommends that or higher for the GTO. Personally, use the lowest grade that doesn't cause ping. Fuel mileage matters to me as well. If I'm looking for a good performer for under 40K that carries 4 people, I'd be more likely to get a 2004 GTO than the 2005 model. I prefer the Mustang over those, but that's beside the point. My daily driver is a "work truck" F-350 Crew Cab. But at least it's got a POWERSTROKE! It gets better mileage than my Mustang. Of course, the Mustang makes more hp than the truck makes torque. Anyway, the Mustang won that comparison. Surely it won't win every comparison, so it hardly matters in the scheme of thngs.