My Rover V8 spark plug experience includes 11 years of ownership and almost 100,000 miles driving my TVR Chimaera, this proved you won't really notice any difference between a nickel or iridium electrode, they're all copper core by the way. In my TVR's RV8 I experimented with NGKs expensive specialist platinum chip ground electrode iridium tipped LPG plugs, BPR6EIX Iridium, and good old BPR6ES.
Having sold many hundreds of gold palladium (precursor to Iridium) plugs during the course of my 20 years in motorcycle spares I agree as mentioned earlier in this thread, they make little difference to a well set up ignition system with copper tipped plugs. However when the chips are down (cold weather, poor battery) these fine tipped plugs, courtesy of exotic metals, will spark at a lower voltage allowing starting when copper tipped will fail. The physics behind this being a spark will jump onto or off a sharp point more readily than a blunt surface - think lightning conductors.
I now understand Iridium plugs last longer as well. The service interval on the Ford Cyclone in my Roadster fitted with these as OE is 100,000 miles!
