Dude, application and particular components. Street, HP/occasional strip or race. Street rockers and some HP will use stock rockers, maybe with brass bushes or steel on steel. But valvetrain loads will not be real high. This includes spring pressures and ramp acceleration rates. High end HP and race likely use rollers lifters and rockers.
As I stated previously, oil pressure is a balance between the oil pump flow volume capacity and the restrictions down stream. Those restrictions are the oil filter, bearing clearances, lifter type and rocker type. Maximum oil pressure is controlled by the pressure relief spring and valve.
Modern engines are designed to run thinner 0/20,5/20, 0/30 oils. The manufacturers also generally recommend synthetic oils due to better lubricity with tighter clearances.
