If you do not use encoder feedback, then the PWM duty cycle controls exactly the PWM duty cycle.
If the load is constant, then a specific duty cycle will correspond to a specific speed.
A specific duty cycle will also correspond to a specific amp draw with constant load, if the motor is either running well, or is perfectly stalled with brushes in contact. For very slow moving motors, the brush mechanism may introduce non-trivial nonlinearities.
If you have a motor with a known current/torque relation, and you can read the present current back, and you can control the duty cycle, then a P (or PID) controller can be a reasonable substitute for constant-torque control.