Since the computer actually controls the air/fuel mixture, setting the fuel pressure hardly does anything as far as performance. It will, however, allow you to get more throughput from small injectors. Injectors are rated at 39psi. If you want your 24# injectors to act like 28# injectors, take 28 multiplied by 39 and then divide by 24. 45.5 psi would give you 28# injectors.
Adjusted Pressure = (Target capacity) * 39 / (Current capacity)
This will only work to a degree since there are physical limitations as to how short a time an injector can be open. As you boost pressure, the computer will try to compensate but since it can't open and close the injector fast enough you will start to run rich at idle.
Changing pressure will only help you with two things. If you are running out of fuel at WOT, boost the pressure. If you think the computer is running too rich at WOT, drop the pressure.
The exception to all this is immediately after you reset your computer. Since the computer has to relearn how much fuel it is dispensing, it will start with stock numbers and start learning what the new numbers should be. If you drop pressure, your car will run lean for a while. If you boost pressure, your car will run rich for a while.
Now to answer your question, set it to 32psi. Those 30#ers are too big as it is. Dropping to 32 psi should have them behave like 24#ers as Mustanguy pointed out.
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351W 89 Mustang GT Convertible