There is no Arduino2 - typical variants are Arduino 2560 or Arduino Due. The 2560 can do around 40000Hz with quadstepping the Due can do 200000 with dual stepping.
QUad stepping does not mean it is always using 4 pulses. As long as you are slow you have 1 pulse per interrupt call, then 2 and at maximum speed up to 4. 1,2,3 steps are no problem it just condenses up to 4 steps in one interrupt call. So we spare the overhead of the interrupt call and just do some more steps so we in total loose less cpu cycles then calling it 4 times in the interval.
