Image a 1/2hp, 24v dc motor, 2000rpm.

Now imagine the same motor, with 48v applied, but with 50% pwm...

It seems to me, the power, torque, speed for either situation
should be the same, but I could be wrong. Sometimes I can almost
convince myself that the torque must be greater in the second situation...

 

Assuming the motor inductance is sufficient to average the PWM pulses at the PWM frequency, then the two conditions should be equivalent.
It's the motor current, not the voltage that determines torque.