just for giggles, i did some timing tests for single digitalWrite() and single steps with speed set to 2147483647 (step_delay is very small at that speed) in 2, 4, and 5 wire mode on my uno r3 and got the following avg timings in microseconds:
single digitalWrite(): 3.4
fast digital write (direct port manipulation): .25
2-wire single-step: 33.53 (29.8k steps/sec)
4-wire single-step: 42.85
5-wire single-step: 46.81
i have no particular question about this, just found it interesting