Yup sounds kind of counter-intuitive, but buck-a-piece copper core plugs are the way to go vs. every expensive plugs I've tried. This is coming from a guy who has most of the them in his 4Banger at one time or another -- Splitfire, Splitfire Triple Platinum, Bosch 4s, Iridium XPs.
I'm not saying these high-dollar plugs won't work a little better than standard, copper-core plugs in other vehicular applications.
But my experience with using them in a 4banger YJ says spend your money elsewhere.