a chip will offer like 5hp and tq maybe.... it a totaly waste and the only way to do it right is a professional dyno tune by someone who knows your car, i would go with fordchip or justin from SCT for the best out there, and you dont need that till you have far more than bolt ons.
diablo chips are junk. SCT from www.velocitymustangperformance.com can get 7hp/tq or more on a stock motor. justin and jason are really good to deal with. they can program to raise the top speed limiter,rev limiter, speedo calibration(99+ only),87or93octane,firm shift points on an auto, and many more parameters. it is a worthwhile investment and if future mods are added justin will be more than happy to reburn it to you specs.
about $350 shipped and customer service is great. if there is a problem they will answer an e-mail within 1 day. i got my SCT chip in 1 week after contacting them. great bunch of guys and very knowledgable