[Hethj7]

Falcons Talon - You are correct in what you are saying. I was more referring to 88fivepointoh's post:

On any High Performance motor, 93 octane is best, you won't always here the detonation, but it doesn't mean its not happening.. If you move up time from stock, 93 is best.


As you pointed out, this statement is true only if you are tuned to run with 93 octane. To just say "if you move time up from stock, 93 is best" is not sound advice. Depending on your set up, altitude, etc., you may be able to run 89 or even 87 octane depending on how far advanced you are.
If you do advance to the point of having detonation occur, try running 89. Just because you have played with the timing does not mean you need to run out and start pumping 93 octane into your ride.

Also, don't just assume that you are tuned for 87 octane at only 10°. That is just a very safe factory setting and many cars can bump up their timing a few degrees and still run 87.

To respond to titanium92's original question, I would say on a basically stock mustang to advance the timing as much as possible while still being able to run 87 octane. IMO, the performance gains on a stock vehicle will be minimal when advancing the timing far enough to warrant running high octane fuels. To me the added cost of the fuel wouldn't justtify the 3 or 4 more HP you might squeeze out of the car.