I used to be an NGK devotee but I've had better service from the Champion 811 (L82C) plug.
One of my engines always was a little sketchy about idleing. I like my engines to idle very slow and that one would just not do it. I switched to the Champion and it will idle like I want it too. It also showed some top end speed increase as well as hill climbing ability. Just to compare I went back to the NGK, a new one by the way, and the engine acted as it did before; no slow idle and a decrease in top end. Changed back to the Champion and the performance followed the plug. Made a believer out of me.
Tom