Years ago, before I got my head back into wrenching, a local indy shop installed Champion copper plugs that fit correctly and were the correct heat range, but they weren't double platinums. They lasted 11,000 miles before misfires cropped up. (That's when I got back into wrenching.) I installed the specified Champions (RC11 PYP B4 for my '99) and all has been good now for 39,000+ miles.

An "authoritative" document I read years ago but now cannot find explained why the wasted spark system used in the DII needs double platinums. Otherwise the electrodes will deteriorate prematurely.

Just go with the specified plugs. Everything else may be snake oil at best.

EDIT: This isn't the doc I recall and it's not written to the same level of tech explanation but it makes the same point.

http://jcwnapa.com/wp-content/upload...11/11-2011.pdf