Jerry,
You are not with me yet. The spinnaker up causes a CE migration, we all agree. With spinnaker up lean the mast back to get the CE at or behind the centerboard to balance the boat, no lee helm. This is what is done today, we all agree. Now take the spinnaker down and the CE of the sloop rig is well behind the centerboard much closer to the rudder. Now the rudder is overloaded and prone to stall. This is what we put up with today.
Here's another way to solve this problem: With the spinnaker up and the CE moved forward, move the centerboard forward to bring the boat in proper balance. Don't rake the mast back. Now we are in good shape with spinnaker up. Now let's take the spinnaker down. The CE moves aft a couple of feet from where it was with spinnaker up. This loads up the rudder and unloads the forward located centerboard. Now, reduce the centerboard area the same percentage that the load on the centerboard has been reduced because of its forward location. This is going to be a number like 10 to 20%. The reduced load on the centerboard now falls on the rudder as an increase in load. Therefore increase the rudder area, rudder balanced, in direct proportion to the increased load it now carries. Now the centerboard is happy and so is the rudder and lee helm with the spinnaker up has been solved. The CE migration dragon has been captured and put in a cage under our control. This will place the centerboard immediately behind the main beam or if you feel bold and run a long spin pole and put the centerboard just in front of the main beam. As the centerboard is located further forward, it is becoming smaller in area and the rudder is becoming larger in area and the system is kept in balance on all points of sail. No more radical mast rake required and no more overloaded rudders with a hair trigger ready to stall sailing to windward.
Bill