Take a look here: Blog : Spark Plug Tech : Stratified Automotive ControlsI have tunes from two VERY well known tuners and they both recommended sticking with stock plugs on the tune. They both do not like the one step colder plugs such as ITV22's. I thought one step colder was a MUST when you tune?
It really depends on your tuner. Just listen to your tuner if they're reputable. I decided to go a step colder and haven't had a single issue, but I'm also tuned by Stratified (author of the article above). Either way, read the article.Take a look here: Blog : Spark Plug Tech : Stratified Automotive Controls
I personally went with the NGK LTR7IX-11's (6510) as I've seen way to many failures of the Denso ITV22's.