I don't want to unnecessarily restrict the flow from my filter, and I agree that we want to have a steady flow (like a few cm/sec) in all of the tank rather than high velocity. Therefore I usually calculate the cross section of my filter tubing (pi*r2), and calculate the spray bar hole diameter that I drill so that the sum of the cross sections of all the holes adds up to about my filter tubing cross section. This in my experience is a nice compromise, and as
@GreggZ says I would drill up holes a bit later if I want to.