FWIW, I went with Sultan of Spark a few years back when I had the 4.2KB setup. I was having spark blowout even with a very tight plug gap. Did the swap and after a few test hits on the dyno, I could adjust the gap considerably larger, thus gained power, but really only the power that I was losing with blow out and tight gap. Nothing over that, from my findings. And better MPG, not that people really care about MPGs on high power cars. lol