I have never made as much power with any NGK plug, on the track, or dyno, although I know guys having success with them. But then again, the two guys that I know that run them are die hard NGK fans, and have never even tried anything else. Mebbie they need a different tune that I have never found.
Side gapping, indexing, and plug brand are the cheapest and easiest ways to a bit more HP. I don't know why anyone wouldn't experiment with those ideas.
The MR43T plugs are prettier than most, with the nickle plating, and are easier to read. I believe the nickle coating is for noncorrosion in a marine app, and the colder range is for continous, high HP running. We just tried them in my pals N2O car, at Mr. Spools recomendation, and it seems to like them.