Well I wouldn't have believed it!
I saw this thread, and wondered if it was time for a new plug. I have an NGK iridium and it'd only done 10k miles on it. However, it'd been running a bit rough and cutting out a bit when cold.
Changed for the Denso IU22 and it's like new again. Well faster than new because it was putting an easy 100mph on the clock again a few tiimes tonight on the way home and it hasn't done that for months.
I'm sure any new plug would've performed as well, but didn't expect to see performance tail off so quick with the iridium.
The plug was coloured spot on too (the old one) so everything else would seem fine.
For �10 off the ebay I'm well chuffed
Rob