I am not responding directly to anyone's comment here.
The way I am thinking about it is this: Pressure is not tangible, it is simply a measurement of something trying to shove something that has volume into something that has a restriction somewhere.
The goal is to keep the fuel rail full so the injectors don't go dry. You need more fuel to do that, aka more volume by having a pump that pumps faster, or moves a larger volume of fuel with each pump.
Pressure is a way to tell if your fuel rail is staying full. It's just a measurement. You want to put more fuel into the rail and also spray more fuel into the cylinder immediately so the pressure doesn't need to increase to solve the more fuel into the cylinder issue. The pressure is just how the system monitors itself like many other systems in the car. Oil, air in your tires, coolant, fuel in the tank.
The only two reasons I am aware of that you need more pressure in the fuel rail are to spray fuel more quickly into the cylinder because your can't get enough out during the injection timeframe, or because the cylinder pressure is so high, the fuel is pushed back into the fuel rail when the injector opens. (this is a real problem on DI systems, if you increase the compression ratio of an engine with DI, you may need to increase fuel rail pressure)
The only reason I would see to increase the fuel rail size is if you want to lower your pressure, or if the pump is not strong enough to jam the fuel into the rail, which could be a possibility, but I think it's unlikely since the pump can't keep the current rail full, again an assumption, does the fuel rail pressure drop? I don't know the symptom of running out of fuel.
This all sounds really familiar... like when we talk about larger turbos, volume of air, and PSI, and charge tube size. Same stuff! "turning up the boost" is done by pushing more volume of air into the same space, which requires the turbo to spin faster, and you hit a point where the turbo is spinning at it's max speed and the RPMs increase which is pulling the air the turbo blows more quickly, so the boost drops. Larger turbo is capable of pushing more air per rotation of the turbine resulting in more air into the same space, higher pressure, more air into the cylinder, more fuel into the cylinder, more power. There is an optimal range of size of charge tube based on the amount of air you are flowing that directs the air in the most efficient way from the turbo to the engine, too small and you restrict, too larger and you spend all your energy filling the tube and not getting it through the tube to the cylinders, I assume the same is true with the fuel rail.
Make sense?
