The difference is in how they get there with the M157 having more torque down low but a shorter rev range. The S63TU out of the M5 on the other hand had a bit less torque down low, a function of its 1.1 liters less of displacement, but a longer rev window by around 1000 rpm. So the M157 has a bit more low end grunt but the S63TU revs higher spending more time above 500 whp. These motors still reflect to a degree traditional BMW and Mercedes approaches with low end torque versus top end revs.
What is clear here is that the standard M157 in 63 AMG without the performance package makes less power than the S63TU in the M5/M6. A comparison will be done between the motors in stock form and with tunes assessing their modification potential as soon as tunes start popping up for the new M5. Dyno graphs are posted below.