I would like to find some carbon metallic pads for my Granada brakes, too. Is that what the taxi pads are made of?
I, too, was a little skeptical, that pad material could make such a big differnce, but on the advise of some other Jag owners I replaced the regular asbsetos based pads on the front and rear of my 95 Jaguar with carbon metallics and can tell you there is an impressive and noticeable difference in feel and performance. The brakes are easier to modulate and the braking certianly feels more powerful. One noticeable improvement has been the lack of brake dust on the wheels.

After 30,000 miles, I don't see any degradation in the rotors.
I also put a set of carbon metallics on the front of my wife's Bonneville. Same improvement. What used to be fairly indifferent pedal feel is now more positive and seems to stop the car better. Again, 30k+ miles and no problems with rotors and dust is not nearly as big a problem.
I can't say what the benefit would be when hot lapping around a track. Your mileage may vary. But if anyone runs across a source for the Granada, let me know, because I'm sold for street use.