""specialty" plugs will produce a less powerful spark than a standard plug will at the same gap. This means that, as long as your ignition system can provide enough voltage to jump the gap on the spark plug all of the time, with these "specialty" plugs installed in your car your engine will produce less power than it will with standard spark plugs"
If you do decide to go with platinum plugs...."The only way you can regain the power lost with these "specialty" plugs is to open their gap out farther (a wider gap requires more voltage to jump the gap).
I've seen a number of cases where people have installed SplitFire, Torquemaster or platinum plugs in their car in the place of standard spark plugs and have complained of reduced power. In all of these cases the specialty plugs were installed using the plug gap specified for the car's original standard plugs (with the exception of the Torquemaster, whose gap is not adjustable). The reduced spark power due to the reduced voltage requirement of these plugs was the culprit."
Platinum vs copper plug link:
http://www.se-r.net/engine/platinum_copper_ngk.html