Will there be any b

 

Benefits of using 91 octane opposed to 87 octane on a bonestock 2000 mustang gt manual tranny?

 

nope! Didn't seem to make a difference in mine.

 

If anything running a higher octane gas in a car that does not require it will hinder fuel mileage and offer no performance gain.

The higher the octane rating the harder the ignition system has to work to ignite the a/f mixture in the cylinder. If you had a tune advancing the timing or higher compression heads/pistons then running a higher octane fuel would be necessary. In a stock car your are best to run what is recommended.

 

Nope. Just wasting money. Stick to 87, unless you get a tune made for a different octane.

 

Just run 87 if you don't have a tune. I would highly recommend getting a tuner though, really wakes up the car. AM is a great place to pick up a SCT tuner since they have free lifetime tunes.