Yes, with ngk the higher number equals colder plug. The more cylinder pressure the colder the plug needs to be.
Your Bov is more than likely your running rich problem. This needs to be recirculated to a point down stream of the maf on a car still equipped with a maf. All of the air that is taken into the engine is accounted for by your maf. When you vent some of the air it has already been accounted for by the computer which fuels your engine accordingly. So now you have less air going to the motor and more fuel. In essence you make a wot pass down the strip, top of the track your throttle blade closes and bov opens venting the excess pressure. The air that you were ingesting into the motor was counted and you're still fueling the motor as if it's ingesting all of that air. This leads to fouled plugs and a rich condition every time. The a/f will look good on accell but will go pig fat on decell. I hope my explanation makes sense, if not let me know.
Sharp looking setup you have there, btw.