look at the latency numbers here
run the test on your own machine, and see if you get similar numbers, and set your base thread period accordingly.
a parallel port driven step/dir type control will always have a severe limitation between the smallest step size ('resolution') and the rapid feed speed. If you need more than a ratio of 10 - 20 000 ( the number of pulses a parallel port can typically push out per second) you should look at other hardware. A mesa pci-card (~200usd/eur) can output step/dir signals in the MHz range.