Slots in the Shroud or Flappers?

[AM.MSCL]

I am getting ready to swap my leaking stock radiator out with a new aluminum one I got.
I already have an electric fan with shroud and figure since I am making the swap I should consider adding some high speed flow through slots or flaps on to the shroud.
In case I have not given enough details about what I am referring to: these allow air to pass through the shroud when you are driving down the highway because there is not enough pass through with the fan running. They also eliminate turbalance from the fan fighting the air being pushed through the radiator from driving 60-80 MPH.
Thanks
Ray