I'm gonna disagree w/ JVT on this one.
while the SAFC does provide some control over a/f ratio (by basically tricking the PCM) it can never effect the ignition timing, which is just as important. Also, the adjustment it does provide is limited, and according to some schools of thought, only temporary, becasue the adaptive nature of the Ford EEC will eventually negate some of the effects of the adjustment (while I tend to agree w/ this line of thought, I have no empirical evidence to back it up, so I only offer it as food for thought)
Bottom line - while the SAFC can be a useful tool in some situations, its method of operation leaves something to be desired, and can only effect half of what you really need to properly tune an engine.
As far as chips go, mail-order chips rarely do much good, as each engine is a little different, as are the conditions each engine sees, so somebody writing a single program for 1000 different engines all over the country also leaves a lot to be desired.
The proper way to handle things, is with a dyno (or in-application) tuned chip done by an experienced and knowledgable calibrator/tuner.
Unfortunately, doing things the right way can be expensive.
