Assuming the 50 HP motor is not overloaded (not obvious from info provided) both motors would perform the same work. The 50 HP would likely be more efficient running closer to its rated capacity than a 75 HP motor runnning at
<2/3 of rated capacity. Table 430-250 indicates 50 HP motor FLA= 65
(460/3/60) so presumably the 50 HP motor is OK. If the machine load increases, the 75 HP motor has 50% more capacity than the 50 HP motor.
