I had some long discussions with Bob on this topic. While there will be differences in the measured results using low ∆P, the benefits of good port work from an accurate flow bench are likely more important than what ∆P is used. Bob's work led the industry when he was using 2 or 3 in/H2O and everyone was running many times that. Bob was a mechanical engineer and highly experienced in using flow benches that were of very high ∆P, much higher than the typical Superflow. I saw test data reports he had from his days at White Diesel, Ford and Chrysler. There's a good reason for going with low ∆P. You don't need soundproof rooms and hearing protection to work on the port while it's flowing. During port development, a technician needs to be able to use probes. High noise hinders concentration and work. With low ∆P, it's not a question of accuracy, but rather whether it is representative of the actual operating conditions. Accuracy is the fidelity of the bench to measure changes and be repeatable. While those early Superflow benches had higher ∆P, they had less ability to measure changes as accurately and repeatably.

The question of whether Bob's bench was representative to real world conditions is exhibited in his succeses at the time, IMO. You can also look at aerodynamic testing. Aero engineers still use subscale test models and low flow rates for a lot of data. My brother is a windtunnel engineer at NASA Langley. And yes, there is a use for high speed tunnel data, but a large portion of data is gathered in low speed testing.