Up until a few years ago I always used 5 or even 5½" feathers on all my arrows. Mainly because that's what everyone else used. Then I was given some 4" parabolic feathers and tried them on my arrows. No difference in accuracy, and they make less noise, so I switched to 4".
The important thing is to get the arrows matched to the bow. If the bow is well tuned (brace height, nocking point, etc.) and the arrows spined correctly the feathers aren't a critical factor.