Re: The spark plugs.
My understanding is that the metal in the spark plug is there for the purpose of channeling the electric current from the wire in the plug to the engine block in the form of a spark.
I believe copper is a more conductive material than iridium or platinum and also doesn't overheat as much as I'm lead to believe the other two materials do.
So:
Copper spark plugs
Upside = More conductive, less likely to overheat meaning less chance of poor spark.
Downside = Need changing more often (in my experience though you can always re-gap them to make them last a little longer ).
Iridium & platinum spark plugs
Upside = Last much longer than copper with iridium having the longest lifespan & best performance.
Downside = Less conductive & more susceptible to overheating.
Not sure what Nissan recommend for the VQ35 but would be interested to know what Mark, Ricky & Alex make on the subject in between helping solve simmo's issues.