Spark plugs.

I've been using iridium on my Vmax and after a few thousand kilometers they are doing fine. Could it be they perform differently depending on the bike?

That could well be the case I can only talk about my experiences.

I used iridium plugs in one of my Hondas. Honestly couldn't tell the difference between them and any other plug I've ever used. If you think about it, in these bikes with dual fire coils, half the spark plugs are sparking in 'reverse' so how much of a factor can the iridium electrode be?