If you track day your car and are always using the power then you will need a colder than standard plug at your level of tune. Most peeps with stage 2+ / 3 on K03 that use the power go for the '8' heat range, as you have the K04 and at your level of tune, the 8 will be fine for fast road / track driving. If you just do normal local road driving the 7 will be fine. The main reason is down to carbon build up. If the plug doesnt get hot enough then it will build carbon up around the electrode, foul and then start running rough. So its down to how you drive and what your needs are.
