Jigga and I are speaking of Zetecs. CSVTs are designed for premium - the Zetec isn't. As a result, it seems the engine doesn't really compensate performance-wise for higher octane. As I said already, MPG improves, but not enough to make it worthy from a $$ standpoint
What year Mustang? I'd guess that older cars with less sensors, computers, etc. would react better simply because they combust fuel and that's it - they don't need to monitor it, smell it, run scientific experiments on it, etc.
