Cabin Master - the PW150 has major differences from the previous models. Now I do not know the PW124/127 on the ATR but I dare say it is similar to the PW123 series on the DH8-300. The PW150 has a 3 stage axial low pressure compressor instead of the radial NL unit on previous designs. Engine control is via FADEC, not via a mechanical fuel control (although on the 123 it is influenced a bit by a electronic control unit). Also the propeller is fundamentally different both in design and its auxiliary systems. And maybe another point important for Your calculations is the fact that the PW150 on the DH8D is not fully rated (the engine is capable of about 7.000SHP) but derated to 5.000SHP. This is very much noticeable when observing ITT values - unlike the PW123 which is often near its limiting ITTs at startup and from takeoff to the top of descent, the PW150 runs much cooler. So please take extrapolated values from previous engine series with a grain of salt.