Solved
If by 300Hz you mean 300 steps per second then I don't see any need to use a HardwareTimer. That rate is well within the capability of simple code using micros()
Have a look at the examples in this Simple Stepper Code - especially the second example. It should be capable of modification to provide a few thousand steps per second.
...R
Stepper Motor Basics
He's done this at least three times so far ... http://forum.arduino.cc/index.php?topic=542684.msg3699743#msg3699743
Don
@JE2555, NEVER EVER delete your questions. The whole purpose of the Forum is to share your knowledge and learning with other people.
...R