Interesting that you should find the plug to make that much difference, keithy2.

I use iridium plugs in my Tenere, WR250R work bike and TTR250 work bike. The Tenere has one because I can convince myself not to put a new plug in every 5 minutes, but I've not really noticed any difference in using it.

The other two have iridium plugs for longevity and to reduce fouling due to running at slow speeds for hours at a time. Particularly the TTR, as it's burning a bit of oil now. It has one grade hotter to help it cope. As with the Tenere, I've not noticed any tangible benefits I could attribute to using iridium, apart from an improvement in fouling resistance.