But the pump is rated at 450lph. Isn't that good enough?

No.

Modern fuel modules use some high-pressure fuel to drive the suction/lift pumps. This amount of fuel is unknown, hence flowrate testing is needed to know the true fuel module output. We have seen +15% of fuel pump output loss due to the need to drive the suction pumps.

The other factor is that a 450lph pump will have a different flowrate for each pressure and input voltage change.

A rule of pumping is that the higher the pressure, the lower the flowrate.

The TI450lph pump, flows 455lph at 30psi/13.5v.

At 60psi/13.5v, the flowrate is 381lph, a 16% reduction in flowrate.