yes it was meant to say "to" and not "top".sorry I'm always doing that typo.
You can test the voltage under load on the road, especially if you have any steep hills, just accelerate in a gear where you get max boost, after connecting some thin wire like speaker cable wire to the fuel pump, then in car to a helpful mate who can watch the voltage whilst you drive flat out up a hill, can do it on the straight and level, just watch out for bizzies!!
If you use thin speaker wire you can bare about 2 inches from the end and put this in the pump plugs before fitting them, so it squashes the cable between the connector and the post it goes on, then through a rear window to metre.
Fuel pressure regulators aren't rated like bhp, they will maintain a certain pressure in the fuel rail, most chippers keep the std pressure to make life easier, the rail doesn't know how much bhp it's running, so long as there is suffecient pressure to start with it will hold it regardless.
tabetha