completly different systems
The RSA is a constant dribble system, 15 PSI would be ample to keep the fuel from boiling but down stream of the servo the fuel system is open into the injector, there is nothing to contain the pressure so it just drains into the intake port. Metering is done by adjusting pressure to an orifice in the injector and by orifice size. So boosting pressure beyond what's needed can't be done without flooding the engine. Pretty crude but reliable and simple.
Any modern car with sequential multiport injection uses computer controlled injectors with 30-40 psi on them to meter the fuel, and timing of the fuel delivery. The pulse time of the injector opening can be precisely controlled via the computer in "closed loop" mode (feed back from the o2 sensor, throttle position, map, temperature etc.) to occur just as the intake valve is opening, and then finely control the mixture by changing the pulse duration based on feed back from various sensors. Pretty cool stuff.
The newest systems, i.e. Direct injection like Fords "ecobboost" using very high fuel pressure can deliver the fuel, finely atomized, directly into the cylinder only when we're ready for combustion. What's cool is pre ignition or detonation risk is gone as there is nothing in the cylinder ignite yet. Turbo boost, compression ratios and ignition timing can now go off the chart allowing much higher power levels than before.
Tim Andres