The 8 is the right iridium. Trust me on this. I went thru a lot of research on the subject before i bought them. As for prformance, there is w/o the slightest shadow of a doubt a gain in power/accelleration compared to the standard NGK's. I actually spend a hour or so one day testing them. i went to a perticular stretch pf road and accellerated thru the gears with each plug a few time. I was actually suprised at how much difference they made. Iwill not go back to standard plug. Some may not notice it, but that doesn't mean it's not true. Some people are not nearly as sensitive to things like this as other. The best way to really see is to do as i did and do it on the same stretch of road because the bike can seem slower or faster depending on the road. Wider roads make the bike feel like it accelerates slower for example.
