Yamaha specced the #8 heat range NGK plug for the early models. They updated that recommendation to the one step hotter #7 NGK on later models. It can be fitted to all models and it is accepted practice to do so. Also, the early spec was for a regular "B" type plug while the later spec, along with the heat range change, also changed to the "BP" (projected tip) type plug. Again, this can also be fitted to all models. I would use the 7's for normal riding, only switching to 8's if I was going to take a trip and be running sustained high speeds and RPMs on the highway. The 7's will give a cleaner burn and better plug color (not as dark) in daily, around town riding.
Something else I'll mention is those Iridium plugs are the resistor type. If you're going to use them, you should change your resistor plug caps to non-resistor types. You only want one instance of resistance in each plug line, plug, cap or wire, not multiple ones. That can add up to too much resistance and start choking off your spark.
