I previously tested the Autolites and they work admirably, I then installed the Denso Iridiums and if anyone thinks a plug can't make a performance difference, welcome to the 21st century, pk up the Denso's, test'em as I did and you'll see exactly what I mean buy a definate increase in throttle response and topend performance. As RPM's increase so does the demand for spark and the Iridiums perform beyond most expectations when in demand. Now my test of the Denso's were also to see how long they would last and it's starting to be apparent that the Ground Electrode is starting to not hold up to the abuse anymore. I'll be installing the NGK Premium Double Plats this week and I'll be able to provide more info in the future. With much more Platinum these plugs will easily out last the Autolite Double Plats two times over, it really just boils down to how fat your wallat is. As a side note there are a number of added features in the NGK Premium plugs that make them a very good choice.
Though Autozone may not sell'em you can surely get the NGK DP through me, I can get pretty much any of the hardest to find street or racing plugs to spark the face of this earth 
