I'd fit a gauge to see what's going on, there's more to oil pressure than the pump - it delivers a volume of oil, the pressure is created by the tight tolerances between the crank and shells (big ends and mains).
Get a hose pipe and hold your thumb over the end, the pressure created will send the the water over a reasonable distance, remove your thumb and the pressure drops as does the distance covered.
Engines don't need massive oil pressure, they do need enough volume to make the crank journals float on the oil without touching the shells that are made of soft lead / tin alloy (white metal). Its difficult to measure oil volume, but really easy / cheap to measure pressure hence why its used industry wide.
I fitted a higher volume oil pump 20 years ago to my 8V GTi, bought from TSR, I think it was meant for a turbo diesel mk2 - the extra volume was needed for the oil feed to the turbo (maybe Vince could help with more info and supply).