Holding torque of steppers is an illusion. So above very slow speed, they will not provide the same as holding torque. Servo motors can provide the rated torque at any speed. Also, servos can provide, typically, 4X rated stall torque for short intervals such as one second to deal with accleration. So, a servo with about 1/2 to 1/4 the continuous torque rating can typically outperform a stepper with that holding torque rating.
BUT, these Teknik "servos" are just closed-loop steppers, so they don't provide that advantage. This can be clearly seen in your graphs, where the torque falls off linearly with speed. The torque at 500 RPM is half of the zero-speed torque. That is pretty awful. The problem with steppers is they have too many poles, requiring the winding current to be reversed too fast. Thus, the inductance limits the rate at which current can be developed in the windings. A typical stepper has 50 poles, A typical brushless servo has 4 or 8 poles. So, making some assumptions, the torque could be maintained to about 12 times higher speed.
Jon