Well under extreme cases the car wont go above a certain rpm because it is blowing the spark out on the plug, other times it might be hard to notice like slightly weakacceleration after a certain rpm. These are the same symptoms if your plug is gapped to far apart or if the electrodes and ground are worn out on a plug. Which Iridiums last a very long time but also look at the ceramic around the iridium tip if its extremely black or gunked over the plug gap is wrong or the plug your runing is to cold. If the ceramic is yellow/orange burnt colored then your plug is getting to hot. A few of the stock plugs had some very light yellowing which means it wouldn't hurt to drop down a heat range when you modify these cars.

I still dont know if my weaker power after 4,400 rpm is plug related but that what i'll try to find out tuesday night at the track.

Not that that my 12.2-12.3 times aren't bad BUT the car has ran 12.0's is 2500 DA so i know somethings off just gotta hunt down the problem.

SIDE NOTE when changing your spark plugs you need a swivel head adapter, 1-3/4 extension, and the back plug on both side you have to assable the 5/8 socket and extension on the plug then attach the socket wrench and swivel head because of the tiny space given back there. Taking the coil pack off to get the plug wires is a pita as well but other than that its not the hardest spark plug job i have done.