Fellow Forum members:
What follows is intended to share information I just came across.  I am in no way affiliated with Street Rodder magazine, M/E Wagner Performance, or involved in the marketing or sale of the aftermarket device described.

Street Rodder magazine
April 2017 issue
Page 112 'The ABCs of PCVs'

M/E Wagner Performance has come -up with an ADJUSTABLE PCV valve.
The one page article states that the purpose of a PCV is to control the vacuum level in the crankcase and provided protection in case of a backfire.

The point is made that while your original PVC valve may have been correct for an OEM application, the valve may no longer be available because of
your engine's vintage OR if your engine has been modified (camshaft or other performance modifications) the PVC flow rates may need to be re-calibrated to work as needed.  Also, the author makes the point that there are no specs to reference for PCV valve selection.

M/E Wagner identifies some issues that can result from having an improper PCV valve for your engine application:
-  Engine idle issues such as unresponsive carb mixture screws,engine can't be adjusted to idle smoothly or unstable idle speed
-  Excessive crankcase pressure perhaps indicated by oil deposits around valve cover breathers after driving or rear main seal leaks
-  Fuel smell in the oil or oil being consumed through the PCV system.

Like a conventional PCV valve, M/E Wagner's Dual Flow PCV valve has two flow rates.  What is unique is that the flow rate for idle AND the flow rate for cruise are individually adjustable. 

To calibrate the valve for your engine application, the engine's vacuum rate at idle is measured with a conventional vacuum gauge and then your vacuum
reading in conjunction with their engine displacement chart indicates a recommended flow adjustment for their PCV valve.

A similar procedure is used to determine and set the transition point for properly adjusting their PCV valve for changeover from idle to cruise mode.

M/E Wagner indicates that additional instruction are provided with their Dual Flow PCV Valve for making custom calibrations or the use of a fixed orifice mode for engines with extremely low vacuum levels at idle.

It sounds to me like this M/E Wagner Dual Flow adjustable PCV valve will take the guesswork out of selecting the correct PCV valve for proper PCV system flow rate with your engine as well as the vacuum level when the valve transitions from engine idle to cruise mode.