Often GM hp is Sae verified. Well the ATS 2.0t is verified and claimed at 272hp and smiler torque yet the 328 n20 dynos as much or more even though its rated at 240hp.
So if the M3 is rated at 415hp, I am willing to bet It will still dyno for more than the 420hp rating of the new 3.6TT.
'98 M Roadster S/C @11-16ps
'06 Saab 9-5 wagon 5mt Aero+ Tuned