I have to agree with maxim, the outer holes won't do any good imo. They will just restrict the waterflow that is coming out of the center jets. I suggest you make some plugs to plug some holes, that way you can test how many holes is the most efficient design. I think you will only need the most central jets since the core is not that big and you will only loose that valuable pressure if you use more jets (no matter the flow rate of your pump).
Well that is at least what i think, i may be completely wrong, i am just one of those 'lurkers'.
