You are operating at a more advanced level than I am familiar with but on the earlier stuff I was involved with the presence of the network inserted a delay in anything going to the printer. Having never traced down what was really happening, I suspect that there was a delay induced to see if anything else was coming for the print job and checking for other possible jobs in the print queue.
Without the network stuff the parallel port was accessable immediately. XP, unfortunately is going to take that ability away from you.