I'd put iridiums on par or ever so slightly better than platinums. And multiple electrodes arre a bad idea. The heat of the spark will keep a single electrode clean just fine, but if you add multiple electrodes, the heat is distributed throughout whichever electrode happens to have a lower resistance at that particular moment. which would lead to 3 fouled electrodes with one that is still being used.
I have seen platinums burn down to below the ceramic insulation before, so I'm testing a set of NGK iridiums in both my Nissan 3L to see how they fare. I'll update ya'll in about 5 years
