Several years ago, several of us car nuts in the Lab lashed up a test rig to measure engine misfires - we found that the Denso Iridium did very well, but were surprised to find that a much cheaper plug, the NGK TR-6, did nearly as well at a fraction of the price. I tried a set of both in my 2003 SVT Cobra.

Below is a similar test nicely done by some of the SVT Lightning gang:

http://www.svtlightnings.com/sparkplugmisfires.htm

 

With the demands of substantially higher RPM spark plug choice may be more limited with the S2000. I would be leary that tests run in a very different environment apply equally to the 9000 rpm world.

 

Weren't they originally designed for sportbikes? And the SVT's redline is a mere 6500, but we saw similar results. So unless something really unusual happens in the last 1700 to 2500 RPM, why would you think the performance of these plugs would not remain similarly excellent?

In our tests, i recall we ran close to 7500 RPM.