since Raj is an EOG (End on Generation) type train, it's weight is less and hence WDP 3A is more than enough for it. Also unlike WDP 4, it has no long hood forward issues being dual cabbed, and so has a high speed rating. WDP 4 in LHF is restricted to 90 or 100 while WDP 3A is cleared for 120 Kmph.
WDP 4D is dual cabbed but its length means that it is given speed certifcate for 105 Kmph.