The octane required by the engine is NOT a matter of opinion. It is predetermined by the manufacturer.
If your referring to my previous post, I own a GT. Minimum octane is 87.
All I was saying is that when I put 91 in, I notice a little better Performance (less lag from a start with the a/c on). Obviously, if you own a GTS and you're putting in anything less than 91, you're asking for trouble.
If you weren't referring to my post, ignore this.