I think the old 300hp crate motor exhaust test is worthless. The cam in the stock Magnum 5.9 (which is the same in the 300hp crate motor) is so small that there were only minor differences in power between them all. But the cam was already limiting the motor so any difference the exhaust made was minor.
So I wouldn't use that test as the standard as to which exhaust manifold is the best on a 383.
