I agree with the above comments about using the plate at speed but i thought this was about the most ecconomical cruise speed etc. Therefore wide open is not the most ecconomical,and at midspeed porpoising shouldn't be an issue? I have a DD so really i could run with or without with only slight difference anyways. My plate usually comes more into play trying to create drag for wakeboarding etc.
On a Vdrive at mid speed porpoising is a reality so using the plate is a must. Remember on a V the engine weight is all the way to the rear.