A slightly nose down condition works well. It means that if the plane shoud stall, the nose will drop, the plane will pick up speed and start flying again. I have tried neautral CG where the nose didn't go up or down with disturbing results. When I stalled a plane with the CG set like this, the plane simply stopped moving forward and started to go straight down like an elevator! I quickly went back to the CG with a slightly nose dwon condition.