Torque Vs RPM
Torque is a function of shaft speed (rpm) and horse power required. Decreasing the shaft speed from 4166 rpm to 3319 would increase the torque that the shaft would experience by 18%. I don’t know the specifics of the dimensions for the upper shaft but I would expect its diameter to be approximately 18% greater that the forward shafts. Form my experience at Sikorsky, I do not remember the Hawk line sharing any parts with the Super Stallions.