the P3 is faster, has better climb/descent rates, and almost double the endurance. I don’t see how cargo carrying ability is very significant for a long duration maritime patrol aircraft.
If I remember correctly the C-130 and P3 both have a conection to the Lockheed Electra.
I suppose if it can carry all that cargo, some internal space can be devoted to more fuel.
I’m not sure how critical climb/descent rates are in an ASW mission...