Stepper motor for robot wheel drive
I took a look on those steppers, but from their datasheets I haven't found the speed. Even from your description there is no mention about the speed of motors, keep in mind that power is a product of torque and speed.
A useful data of stepper motor is back EMF voltage V/krpm, which in both models is absent. 34mH has more turns than 2.8mH and higher BEMF voltage respectively. At 12V they won't reach the same final speed, also the dynamics is different - the 2.8mH is faster in terms of dynamics and it will reach higher rpms at 12V, but less torque than the 34mH model. The 34mH would be high torque , low speed motor.