Easy to find out your fuel pump capacity.
Disconnect the
*Return line* after the fuel pressure regulator. Before it goes back into the tank, and put it into a 2 liter juice bottle. Hardire the pump to a good 12V source, voltage has a lot to do with performance of the fuel pump so make sure its getting a solid 12v-13v for the test. and record the running voltage across the pump terminals, whatever it is, as part of your data.
With the fuel pump on any bypassed fuel will run into the 2 liter bottle. Is it important you accurately measure the amount of time it takes for this bottle to fill up. With this data you can work out the flow rate of your pump at rail pressure and form here you can work out maximum supportable horsepower.
Important relationships to note:
Less voltage at the pump = less flow
More rail pressure = less flow
If you do this please post the data in here so we can all use it