I am of the opinion that HV oil pumps are not needed on anything but full race vehicles. I get this from all the reading I've done concerning engine building. Basically, the extra hp lost turning that HV oil pump would be better put to use moving the car. The reason you bring up is another. I learned that from my old neighbor (who had been building race engines. real race engines), and my uncle (who is an ASE diesel tech).
A good blueprinted OEM volume pump should be as much as anyone streeting would need. Mazda engineers knew the engine was gonna go to 6000rpm. and that people buying the GT would prbably spend some time there. Do you think they were gonna let it starve for oil?