I am now going with a Champian L86c and I love the new sound I seem to be getting.
The plug is a bit too long and I may end up with probs. when I go to remove it but it did change the sound and feel of the bike, almost as if it is running a little richer now, from the sound of things. I have also used the "40501" which is what I seem to remember being an NGK but looking at it now, there is no "ngk" marking.