Most injectors are rated at 43.5 psi, however Ford has setup the EEC for about 40 psi static. I've got the MSD 50s in my car and pressure is set to 40 psi and the car has been tuned at that setting. I know other guys running 45 psi static with the same injectors. I perfer the lower static setting so my fuel pump will still be able to keep up at peak pressure and flow. If you raise the base to high say, 50psi and add 15 pounds of boost, the pump must be able to maintain rated flow at 65 psi...most pumps won't and you go lean on the top end.
Just about any injector you choose to install will work fine at 40 psi, the only exception I ran across were Lucas 38# injectors, they had to be set at 43-44 psi or the engine bogged from a stop.
Set the static pressure with the vacuum boost refrence line removed and plugged with engine idling.
David