cant answet that - simply went with advice I received from a) respected members of this SAU community such as Sydneykid when I first joined 2yrs ago, and b) tuner advice
I thought bumping up fuel presure by a psi or two is like, to a certain point of view, say making the injectors flow that little bit more than normal at the same duty cycle.
ie 80% duty cycle a set of six injectors may flow XXX. bump up fuel pressure and the duty cycle comes down to say 78% at XXX rate of flow. tune the engine and get back to 80% duty cycle, and youd be using more fuel (plus more air) thus getting more power from the exact same 80% duty cycle from the injectors.
Im not a mechanic, but I thought that an adjudtable FPR such as the Nismo item is a good solid modification to perform, rather than going to larger injectors (when not looking to increase power at the engine thricefold, ie from 120rwkw to 300rwkw with injectors and full ecu/mods, in lieu of 120rwkw to 220rwkw with stock injectors and dodgy ecu/mods)
in other words I have no idea ! :laughing-smiley-014: gary said it would be a good addition to my fueling system, so I got one.