I was reading awhile ago on some Supra forum about guys who turbo their 5MGEs, they slap 12:1 RRFPRs on them and some weird piggyback fuel controller to tweak the fueling, so they can make 400hp on factory 172cc injectors and stock ECU.
I thought that was fucking stupid.
The factory FPR should be more than mint up to 10 odd PSI, after that they can get a bit sketchy as they were never designed to take that much positive pressure, unless you raid one from a factory turbo car.
In any case, if you have an aftermarket ECU and injectors that can flow enough fuel to match your power output, a 1:1 or thereabouts is perfectly lush. The only reason you ramp the fuel pressure up more is because you are too cheap to buy better injectors.