http://www.gassavers.org/showthread....ght=spark+plug
my good friend Diamond Larry did some testing of different spark plugs. no appreciable gain from one to the next. true, all vehicles react differently to different mods, but i doubt spark plugs will yield measurable gains in any app.
rule of thumb(for me personally)...
buy the OEM or cheapest plug you can find on 4 cyl cars (and easy to change plugs on 6 and 8 cyl). however, for difficult to reach plugs(like my wife's camaro), i use a long lasting platinum(or similar) plug to avoid changing them as often.