High volume pumps are generally not needed if the bottom end is assembled to factory clearances. If the stock pump delivers adequate volume (and it will), any additional volume will just be diverted back into the pan via the bypass valve. So at this point you are just wasting horsepower to pump oil back into the pan. This puts excessive loads on the timing chain, cam and intermediate shaft.
Here's a little experiment to try on a running engine. Once up to temperature, and with a reasonable (10w30) weight oil, note your oil pressure at idle. Now, slowly increase RPM watching the oil pressure gauge. Pressure will rise in a more or less linear relationship with RPM to a certain point and then level off. This point pressure levels off is where the pump begins to deliver more volume than the engine can use and the bypass opens. You can raise the level off pressure by increasing the spring tension on the bypass valve. So, if you peak at 55 PSI at 2500 RPM, a higher tension spring can raise you to 65 PSI which should be adequate for street and bracket racing. Now if you don't peak, or the oil pressure remains below the 10 PSI/1000 RPM curve, your engine requires more oil than the pump can deliver. Or even worse, if pressure drops off again at high RPM indicating excessive rod bearing clearance. So, to lower the RPM where your oil pressure peaks you either have to reduce demand (clearances) or increase pump volume.
Remember that while the output of a constant displacement, constant volume pump increases in a linear relationship to RPM (that is they are directly proportional), the work required to deliver increases exponentially. So using arbitrary figures as an example, if the pump requires 1 horsepower to deliver 10 GPH at 1000 RPM, it will require 4 horsepower to deliver 20 GPH at 2000 RPM. So there really can be too much of a good thing.
In an ideal world, your pressure would continue to rise with RPM and peak at the highest RPM you run. For example, 65 PSI at 6500 RPM as you pass through the traps at the end of the track. This way you are assured adequate oil without wasting energy pumping it in circles.
Why not just run thicker oil to increase pressure? Viscosity is defined as a liquids resistance to flow. So it will just take more work (horsepower) to generate the same pressure. Also, oil pressure is measured upstream of all demand. A thicker oil will experience a greater pressure drop throughout the oil passages in the block and crank. This is why ATF and most hydraulic fluids are 10 weight at most.
