If you lived someplace where the speed limits were much higher, or there was little enforcement, and you ran your bike at nearly full throttle for, say, a half hour at a time, you'd maybe want to run a cooler plug. In normal use, no reason to run a colder plug. I rather suspect, in this age of electronic ignition and fuel injection that spark plug choice is much less critical than in the old days of carbs and points, when mixture was all over the map and ignition was a some-times thing. Wouldn't surprise me greatly to find that modern plugs also work better under a wider range of conditions, especially the premium plugs with small-wire electrodes. Probably one of those things that, if it's working, don't mess with it.