I've been using 5" parabolic for a long time now but in the 60s I used shield cut. I can't tell a difference between the two from the shooters side of the bow. Someone on one of the forums did a sound test between the two but I forgot the results. I also had my wife stand behind the screen door and I shot a bunch of arrows with parabolics past the door about 2' from her and she said she couldn't hear anything but the arrows hitting the target, not even the bow.
With 75-80 parabolics left I'll just use them up and then switch to shield for variety.