We just experiment with different valves... or take the info that others provide.... like in this thread. You can take the hose for the PCV to base of the carb in hand, and swap different PCV's on and actually feel and hear the flow difference.
If your PCV has a higher transition vacuum level than your idle vacuum, then it is dumping in more air at idle and you may well be able to compensate for that. But then you apply a bit of throttle and the revs come up a bit, and low and behold, your vacuum is now ABOVE the transition level at mild throttle operation when you are moving out from as top sign, and the PCV flows DROPS. Your transition operation is going to be messed up due to the change in air flow when it shouldn't and with the idle compensation you did to make it idle in the first place. The carb designers are not expecting the PCV flow to change in a backwards fashion with light throttle.
You can cause lots of off-idle stumbles with the wrong PCV vs your cam, and then mess with other things like timing that you shouldn't mess with to compensate for it.