The "Throw Away 318"

Every HV pump also has the heaver 'By-Pass' spring so it will not go by pass as soon.

There are many Dyno run tests of just HV pumps out there. I wish I had the Dyno sheets to show. The Dyno tests I was involved in were on a mild 451 stroker 400 block with its external pump. They did these runs with a standard volume and bypass spring then changed the pressure relief spring up till 80 PSI and lost 15 HP from base.
Then a HV with its spring it came with and lost 25 HP from base. It was pushing 85 PSI. Then we replaced the spring so we had 50 PSI at idle hot and it still lost 15 HP.