1.5x more speed = Agfa-47 need 1.5 times less time than D-76 for developing film to same ISO. In case Kodak Double-X @250 - 7.5min in D-76 and 5min in Agfa-47. I guess that 7.5min in Agfa-47 will be good for 400 ISO, but contrast may be very high and not acceptable - I can't test this combination.