questions about tuning

Most people will benefit from a chip/tuner/custom tune. The factory tune settings are pretty conservative to keep the car pollution friendly and people can run on 87 octane gas. An aftermarket tune (whether it's through a chip or a flash tuner) will give up some of the pollution control friendliness for some power. From what I've read, the aftermarket tunes will 1) advance the timing, which requires you to run higher octane gas, 2) lean out the a/f ratio, but giving up some of the smog friendliness. My understanding is the factory a/f ratio setting is a little on the rich side to keep the cats from overheating.

Since you already have a TA, you might not see the full benefit of an aftermarket tune/chip. You probably have your timing advanced already.

The tune cannot correct your a/f ratio unless you send them a print out of a dyno run that includes a wideband a/f reading when you order an SCT Xcalibrator. Or, you can adjust it yourself (as much as you like) if you have a DiabloSport Predator.

The 4-position chip, or any flip-chip is good for those that run nitrous. You can switch between the non-nitrous setting to the nitrous setting right as you stage. If you don't see a need for an instant tune change, then the handheld tuners will let you make changes yourself and flash the EEC in a 5-10 minute process. Unless you have a specialized application, like a blower or turbo or aggressive cams, you get more bang for the buck with handheld tuners vs chips.