I built my NCs long before the RB sways for MX5 were available. And, I am running much more bar than most folks will want....because I am running much more grip. Thus, our supercharged 2007 has a Racing Beat bar....but it is the RX8 32mm front, and that is matched with the massive Hotchkis rear bar.
However, have used the new Racing Beat MX5 sways on several customer cars and tried them for autocross and track and for those running more reasonable levels of grip (like STR levels of grip for example, typically 17x8 to 17x9 with 235 to 255mm wide tire sizes), they work great. Most are starting with the center hole and I tried the center hole front and the tighter inner hole rear and I liked that balance on the STR car I tried. Bottom line is that NOBODY can tell you the "right" holes to use because balance is a personal preference issue. Some like a "pointy" car, that rotates on lift (that's how I set mine up), but others prefer a light understeer at the limit. Other variables include what spring package you are running, what shocks, the tires, the alignment, etc. The best I can suggest is that you experiment with the settings to find what YOU like.