You'll get a few more HP or maybe 0.5 MPG more with a light right foot, but nothing that'll knock your socks off. Mark designed the Tornado chips essentially to improve the mid range lean map on the GEMS P38 in an effort to prevent the slipped liner issue possibly contributed to by lean burn when on cruise, i.e. light throttle motorway driving which causes, in his opinion, the engine to operate too lean and too hot. My Thor 4.6 also slipped it's liners though.......(maybe the Thor MAP is also lean, hmmm). I ran them in my '98 4.6 with stainless sports exhaust and while I don't regret buying them, was pleased to sell them once removed from the car for £450 when I sold the car. If you have £650 burning a hole in your pocket, go for it!