Not anymore since installing a surge tank, but before running 1.7bar of boost, a single 450Lph Walbro, I was doing 372kW at the tread.
However in saying that, I did have fuel return issues. Even with the FPR fully wound out, I would still get 2 bar of fuel pressure. Back then I wasn't running a fuel pressure sensor so can't tell you if there were issues with fuel pulsation - which I suspect was probable due to weird lean spots in my fuel map.
Now I use both lines (OEM feed and return) as only a return and fuel is fed to the rail via a 8AN.