After I installed the supercharger I had some slight detonation problems, but a set of Denso Irridium plugs took care of that. I was running the stock E7 heads then.
Last year I installed Trick Flow alu heads and went with a set of NGK copper plugs instead of the Denso plugs and they seem to work just fine. No detonation at least.
I remember the irridium plugs were incredibly expensive, but on the plus side they also had extremely long replacement intervals.
Anyways, I dont think you will gain any performance with irridium plugs, but if you are running high boost/spray then they may help with detonation/pinging.
Otherwise I would say go with good quality copper plugs.