im pulling 371hp and my mechanic/tuner told me to use coppers, he said, "replace them every 4-5000kms, they are $2 each, who gives a f$%k" i just gap them to about 0.8mm (from memory) and im set..
IMO id rather spend $12 on a set of plugs than almost $100... i can buy 8 sets of copper plugs to one set of those fancy ones. 8 sets will last me 40000kms... by the time i reach that distance on my odo, ill prob have wrapped teh car around a tree...
copper = winner