I've had a couple 4-bank chips installed on my '95. The throttle response is better (of course), it idles a bit higher (closer to 950 compared to about 700-750 with the stock tune). It felt noticeably quicker after the install. My car currently has just minor bolt-ons. One of the reasons I purchased it was because I deleted the EGR and was too lazy to make one of those delete resistor plugs. The gas mileage plummeted as I chose the "performance" tune.
Based on my experience, I would recommend passing on the mail-order tunes and either going with the quarter horse or having someone tune it in real time. While I'm not completely dissatisfied with the results of installing the 4-bank on my car, I know that it's no where near as good as it could be.