I add drainbacks and drill the main feeds in everything. The enlarged main passages have nothing to do with needing more volume from the pump. Bearing clearances and type of bearings have everything to do with needing more volume. If you are running stock spec clearances (up to .0025") then a stock volume pump with a high pressure relief valve is fine. If the clearances are bigger than .0025, and you're running full groove main bearings, then the HV pump will be needed depending on the performance expectations. Consult your builder on the clearances prior to anything being machined.
