WDP4 is comparably better with longer trains. WDM3A locos are usually not given to trains with more than 20 coaches as their horsepower isn't enough to accelerate well with longer trains. WDP4 unfortunately struggles on steep gradients with longer trains as it was designed to haul 18 coaches at good speeds. WDP4B/4D locos are the best diesel locos of IR which can handle the long passenger trains anywhere.