I' ve been shooting 4 4" feathers set at 90 degrees out of my recurves for a number of years now. IMO, they stabilize faster, and are more user-friendly with not having to worry about a cock feather.
Arthur, I just got a feather chopper (LONG overdue). I can get two 4" parabolics out of one full length feather. It' s actually cheaper for me to do four fletch this way.
JRW