I don't have the stock setup as you know. My water pressure is around 10 psi cruising and 15 psi at WOT. I have no t-stat and use a water x-over so water goes in block,thru heads and out to exhaust.
There was a thread out here about 9 mos. ago and somebody made a dump valve or bypass because his water pressure was around 50 psi. He set it up to dump excess pressure thru a hull fitting. Try doing a search. I think the thread was started by someone with "fountain" in his screen name but don't quote me on that. If I think of anything else I'll let you know. What is your current water pressure? How are you getting your reading? Is it a mechanical or electric guage?