The logical next step after recording the pre-turbo pressure loss with the RS4 intake components on a Stage 3 setup, operating around 24 psi, was to swap the RS4 Y-pipe out and replace it with the S4 Y-pipe.
A comparison of pre-turbocharger pressure loss recorded with these two Y-pipes is shown below:
Expressed as a percentage increase in pressure drop when going from the RS4 to S4 Y-pipe the results look like:
The boost and MAF readings for these two cases is presented in the chart below:
While there clearly is a measurable gain in using the RS4 Y-pipe instead of the S4 Y-pipe it is unclear if the difference would translate into a performance increase for the engine.