Glad to hear that the Carbotech love is spreading
They know how to make a great pad for sure. I did not see what type of street tires you were using from your original post, but I can confirm that you very likely have too much pad for the street on the tires you are using. My experience has shown that XP8's work best with true street tires (like the RE11 or Dunlop Star Specs) and the compound should be increased as the tire grip is increasing as well. Especially once on track, you will find that your XP10's up front will work very well with R888's or NT01's. Even with street tires though, a car like the 370Z could still use the XP10's for the front on track.