I am also running my race ported P5XS in an RC8 with a 7.25mm insert, a JP1, RB Concepts 8 cold plug and TQ 30/12 and I am averaging 9-10 minutes on a tank depending on temp, humidity and of course driving style. You should be getting at least 7-8 minutes with the stock 8mm insert. Not sure where you run, how you drive and how you tune motors but that should be your target number.