Note entirely. Both platinum and iridium deal with heat better. As a result, they can be run 'hotter' without as much concern for preignition. That means the plugs stay cleaner, and they also stay sharper longer - which means better spark for longer, or better spark with a 'hotter' ignition system longer than a copper plug would last. It also means that they deal with non-ideal conditions better since the plugs are better able to fire with increased EGR, sub-optimal AFR, and will put up with abuse for much longer than copper.
My take is this: tune with copper, fine-tune with platinum or iridium after and then enjoy the car. There's no reason to run a tuned-up engine with anything but platinum or iridium, especially with a souped up ignition (MSD, etc). IMO: copper doesn't last, doesn't stay in-tune (no one replaces plugs before fiddling with the carb), and aren't well suited to anything but stock applications. As soon as you have more spark, more cam, more abuse, copper just stops making sense.
