How to determine a safe red-line?

Hold it floored til it blows up....rebuild it and take 500 rpm off....I have never put a lot of stock in the 1k/10psi thing. Had a motor built by the best, at the time, race shop in NJ. Was a little 2.8 v-6 in a Bronco II. Never seen over 20psi or so of oil pressure. Put over 400k on that motor, never had a problem.