Dodge,

How could this be determined? I had similar concerns by going to this big of a pump.

the trend in injection has been 55-58 psi like the returnless systems out there nowadays. With the newer style injectors they work really well with the higher base pressures.

Stock 502 MPI is around 41-43 lbs,

He's running a stock 502 MPI

As a follow up, I checked my return plumbing setup and I am returning the fuel thru a pickup.

Heat builds every time something is under pressure. Even Aeromotive has mentioned it may need a cooler depending on how much fuel is actually used. So if your not using most of the fuel running WOT it just keeps bypassing more warm fuel. Over time it "could" get to warm and start causing issues with fuel burn. What those issues would be I'm not sure and would just be guessing, no expert here. My guess would be fuel may start to burn before the spark ignites it, then there is preignition.

My motor dyno was at 530hp using Merc cool fuel module. Running higher fuel pressure would figure shorter ON times then lets say 40 psi

Note: could use a smaller pump and same reg to just push less GPH. Same pressure but less volume

I'm using an Aeromotive 1000 pump on a carbed procharger set up. I run the return fuel through a 2 x 9 inch cooler on the way back to the tank. works just fine. returns to the top of the tank and just pisses down into the tank.
Just an FYI

I used to run Aeromotive 1000's with a controller that varied voltage to the pump depending on rpm. I recently set up new motors again using 1000's but adjusted pump output again based on rpm. Kind of a PIA but I believe it is easier on the pump and keeps fuel temps down. Used with Kinsler injection and carburation. In all cases returning fuel to tank. Never have had a pump or controller fail. Good stuff!

Guess I just miss the reasoning, but why use a 1000 when a smaller pump will provide everything needed?

I believe a normal pump operates at a constant speed when it gets 12+ volts. So at idle, it may be pumping at a rate exceeding what you require at idle, creating excess pressure and subsequently heat. However, at WOT you may need that flow capacity. Some pumps provide a controller that allows you to reduce the current flow to the pump at lower rpm or loads when you don't need the fuel flow but are able to increase their flow capacity at WOT or higher load demands.