Yeah, I know all about the pressure/volume debate...my main concern (in my setup) was the FASS over-pressuring something like a seal...I also was reading Tomeyguns findings about the fuel rail relief valve issue...since I'm not modified, that shouldn't be a concern.
I know too little volume is bad, but at the same time volume and pressure are sorta the same...I guess it also depends on where you take your pressure readings at too...you could be seeing "good" pressure upstream near the pump and low pressure (and volume) downstream because of inline restrictions (ie small lines, restrictive banjo fittings, plugged filter, etc.). I think the general concensus is that the factory fuel system is just barely adequate, but to get the optimum fuel system...you build/buy your own!
With this 13psi spring, I got 12psi. I took the truck for a test "run" and basically did several 100mph "onramp" traffic merges in 5th and 6th (these were also upgrade pulls)...I also have a low pressure light in the cab (the gauge is out next to the CP3, the light's sender is on the pump)...it never flickered so I can a$$ume that the pressure isn't dropping to 7psi...and that should provide plenty of fuel (through a 3/8" hose) to the CP3 hopefully.
It still runs better than it did with the factory fuel delivery system!
steved