Holley doesn't list specs on the pump so you have to go to the Tanks Inc website. Tanks Inc does an excellent job listing specs and even shows a flow vs. pressure chart with different voltage and amp draws.

The GPA-4 which is the 255 lph pump will deliver 65 gph at 60 psi if the alternator is working (13.5 volt system).

65 gph is 390 lbs/hour which is enough fuel for 800 hp. So I don't see any reason to use anything bigger than the 255 lph pump for the normal Mopar stroker engine. You would need to be running a monster of an engine on the street to need the 400 lph pump.