Things I've learned about spark plugs:
Copper plugs will produce just as good a spark as a platinum or double platnium. The only difference is longevity. Platinum plugs will last up to 2 or 3 times the lifespan of a copper plug. This is because every time the plug fires, a microscopic amount of metal is vaporized.
The gap on a standard spark plug grows about 0.000126 in. for every 1,000 miles of normal driving. And the wider the gap, the greater the voltage needed to jump the gap. On standard plugs, the firing voltage requirements creep up about 500 volts for every 10,000 to 15,000 miles of driving. Eventually, the plug may need more volts to fire than the coil can produce, causing the plug to misfire.
Platinum is much more resistant to the vaporizing effects of the spark, to the point that using platinum almost eliminates electrode wear.
single platinum plugs have one electrode surface made with platinum. (generally the base electrode, which runs much hotter) Double platinum plugs have both surfaces made of platinum..
One thing to keep in mind about all "performance" spark plug designs is that no plug can magically create horsepower out of thin air or add horsepower that wasn't there in the first place. But improved ignition reliability can minimize horsepower losses caused by misfires. That's why some plug manufacturers claim their spark plugs improve power. The gains come from power that was being lost to misfires.
Good plug wires are just as important to ignition performance as the spark plugs. If the full voltage doesn't make it to the plug, misfires could happen, especially with 'aging' spark plugs.
Iridium plugs take the diference between copper and platnium up to the next step in terms of longevity.
I use NGK Iridium IX plugs in my ranger , mainly because I won't have to worry about replacing them for 100K miles.