i have ngk iridiums and i only paid like $52 for them shipped (not too bad imo)
i read an article, dont remember where right now, but the dyno showed a .2 hp increase. (hey any increase is good!)
also i dont know if just coincidence but i was running consistent 14.5x's at the track, after the plugs i was able to pull a couple hundredths and squeeze a 14.47 or something....
regardless of the power gains or et, the car runs so much better and is much smoother with the NGK. If you want overkill, go Denso