I tend to shoot either 4" parabolics or 4.750" shields......right now I'm using shields. My only real noticeable difference it the longer shields tend to stabilize a larger profile broadhead a bit better, but there's probably some here who would disagree with that statement. Just my personal prefference is all, and basically that's probably what it will come down to for you?
Try the shorter feathers for awhile and if you don't get along with them or they don't stabilize your BH's then simply switch back to what works.
I would suggest only refletching one of your arrows first or maybe two?
Just in case you decide to go back to the originals.