It's not really bhp dependant, it would be boost pressure dependant as the fuel pressure incresases with boost pressure. With a 1:1 rising rate fuel pressure regulator, and assuming the base fuel pressure is set to 3.5 bar at 0 bar boost, then 1 bar of boost would give fuel pressure of 4.5 bar, 2 bar of boost would be 5.5 bar etc.
When it comes to fuel lines I would over spec any joints by a big margin, you don't want high pressure fuel spraying anyware near hot engines / turbos / exhausts!