Andy - pure race engines are built with far larger bearing clearances than street engines. This is because they are seeking to minimise friction, and don't care about the trade-off in longevity.
In that situation, a pump capable of moving higher volumes of
oil than std is needed to maintain pressure in the system, and hence maintain the
oil film at high rpm in critical bearing areas like mains and rods.
In a street engine, the bearing clearances are smaller. Less
oil volume is needed. The std oil pump has more than enough "volume" capacity to cope. (You would probably find that even with a std oil pump, more oil escapes through the pressure relief valve than goes through the bearings anyway).
The power required to drive the oil pump comes through the distributor drive gear from the cam and down through the oil pump drive shaft (buy an uprated one incidentally) via the hexagonal hole in the bottom of the distributor drive shaft. This is one area of potential failure on the Ford SB, and putting a HV pump on increases the power needed to drive the pump, hence increases the chances of distributor drive gear failure.
Since a broken dizzy drive gear means an engine strip down to get rid of metallic debris, it is worth taking steps to minimise the potential for failure in this area.
IMHO, HV oil pumps in street engines fall into the "bragging rights" area.
Phew. HTH.
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