The compression ratio of your engine determines the octane required. The compression ratio in a stock GT is not high enough to require anything above 87 octane. Many high-performance engines are designed to operate with a high maximum compression, and thus demand high-octane premium gasoline. I'm pretty sure that the Cobras, for example, require premium fuel.
Unless you've added some performance mods (i.e Tuner, Forced Induction) you will see no real gains by using a higher octane.
__________________ 2002 Mustang GT auto: SLP LM1, 8" shorty antenna, grille delete, coin delete, Cervini front bumper, SCT SF3 93 octane, JLT RAI, Professional Products 75mm TB and Plenum, FRPP 4.10, 10.5x17 DD Bullits, Nitto 555R's
1/4 in 13.828 @ 99.13
"American muscle needs a healthy diet of Foreign rice." | 
Fuel preference 
You're just taking up space and bogging down the site.
