The high pressure pump has a stiffer release spring. At low RPM if you are dealing with low OP that won't help. The relief valve is already closed. The high volume pump will move more oil at low RPM and may help oil pressure.

The only application I can think of where a high pressure/std volume pump may help is a super high RPM race engine (>7,000 RPM).

Otherwise the HV/std pressure may help a low OP situation at low RPM... and as many have posted the std volume/std pressure setup is usually fine with a stock or near stock engine.