About 4 years ago, I added a fuel pressure sensor, to my fuel system and fed its output into the megasquirt. To do this, I removed the pressure regulator from the fuel line, and mounted it in a block of aluminum that also houses the sensor. Here's a pic (the fuel system returns fuel to the tank).
When running 460 injectors, and in boost, there would be a 1psi ripple on the datalogged output. Three years ago, I upgraded to 550 injectors and found that this ripple increased to just a bit over 2psi. Recently, I upgraded to 750cc injectors. Check the datalog below to see how the measured pressure is jumping around (the white line in the lowest section). From the peak to the trough, there is a 5psi difference at some rpms.
I replaced my fuel filter, confirmed that my walbro was getting full voltage, tried disconnecting the pressure line to the regulator, added a few filter caps on the output of the pressure sensor. Couldn't get the pressure reading looking smooth.
Recently I purchased a M-Tuned fuel rail. Mark at M-Tuned, suggested that I run a NB pressure damper in the rail, even though this was a return system. After installation, with the damper, the pressure variation is still there, but reduced.
So, as many on this forum have previously stated (over and over again, which I managed to ignore), you should strongly consider upgrading your fuel rail if your north of 200hp.