As for fuel injector cleaner, never found anything that worked better than the type that you pressurize and connect to your fuel line, disabling the fuel pump - and running the engine off of that alone - never noticed a performance or gas mileage increase using any in-tank 'fuel injector cleaners'
However, Ford does recommend using chevron techron on the 05+ mustangs when they have fuel gauge/sender problems, and it did seem to cure the problem (at least temporarily), so they must do something, even if minimal
as for octane:
Octane Booster Reviews
That links to a site I found very useful when setting up a track tune when I didn't feel like wasting $ on race fuel - plus it was readily available when I was tuning, race fuel was only available about 30 minutes from here -
I was able to add ~1.5* timing across the entire RPM range using a slightly higher than recommended dose of Torco -
Also, another link.. this can be found in the form of paint thinners at home improvement stores.. (toulene and xylene)
Homebrew Octane Boosters
Hope this helps some..