Be careful; most Iriduim plugs do not have an Iridium ground electrode - only a center electrode. So if you got one of those brands, they will probably start misfiring pretty soon.
Double-platinum is recommended for the Duratec with good reason - because BOTH electrodes are platinum, not just the center electrode. It's the only solution for long-term reliability with the Duratec's waste-spark system, which fires in BOTH directions and will quickly devour any other type of plug.
