If your arrows are tuned well, four inch is plenty to stabilize them. You will gain some speed. I don't notice that they are any quieter. I have used 3x4", 3x5", 3x5.5" and 4x5", both parabolic and shield. The more feather you use, the slower they fly. They are more stable in still conditions, but I think the larger feathers drift worse in a crosswind.
Despite their negatives, big, shield cut feathers look cool though, and I still like them on woodies. For well tuned carbons, I'll probably use four inch three or four fletch. For aluminum 3x4 or 3x5.