Yes, the stock ones are double plat's. I heard though I think from Fast Ed N (Correct me if I'm wrong please) that the double plat's have been discontinued by Ford. I've got a set of iridiums on the way and will get them installed in a couple weeks. From what I've seen, the iridiums are better than the platinum as the material (Iridium, go figure...) is stronger, conducts electricity better, and has a high melting point than platinum. The biggest advantage is the ability to conduct electricity better. The iridium plugs actually take less energy to fire than platinum plugs. That translates in to better performance and durability of the ignition system. And the iridium plugs can be had for about the same price as the double plats. I paid $6.95 per plug for the iridiums and paid (foolishly) $10.00 for the *double plats (I'm not sure that they actually are the double plats). That was about a year and a half ago, and now I've got to replace them again.
I do know that there are several people on the boards who are running the iridium plugs and are very satisfied with the results. And this is in high powered SC's.