Which plugs are best for performance?

I can speak to longevity.
My RN12YCs have been in my 367 since 1999.
I regapped them in 2004. Currently, the total is over 100,000 miles. I bought a new set in around 2010,but they are still in the tune-up kit I keep in the trunk, where also are; all manner of carb and dizzy parts, as well as the obligatory spare ballast,a flashlight, a knife, zip-ties,assorted wire connectors,fuses, some tools,and a bagged half roll of azzwhipe.
If you have a decent tune,and a decent coil, you can fire just about anything, I guess.
These plugs have made just one 1/4 mile pass, and just four 1/8 mile passes, and hundreds, and hundreds, and hundreds of 2 and 3 gear runs with the tach pegged to between 7000 and 7200. They have driven several thousands of hiway miles on trips, and the rest was just bombing around and having fun, between May long-weekend and September Long. Oh,and probably many,many hours of idling and low-speed messing around. And no CDI,either.
I couldn't give a hoot about what conducts better, as it pertains to plugs.
I worked in a bike shop for something like two decades, and have seen tons of bad NGKs ,many,right out of the box. Some just flat quit under power, and some would not recover from being flooded, even tho brand new a couple of hours prior. I'm in no way ragging on them, cuz I also installed thousands that never had a problem.
I've also seen some of the crappiest coils ever produced that would look for any old excuse to quit firing.
Get a good coil, and it doesn't care what plug is on the other end of the wire.