Ed Moorman did a test on sticks by removing the traditional tapered stick wingtips and adding fences (about 3/8" high all the way round) to the flat tip ribs. It lowered the stall speed and really increased the roll rate, but the plane wouldn't spin well. Hard to stall into the spin. Made the airflow over the wing more laminar thus making the ailerons have more effect. After I beat up my stick(still shiny new!!) some I'm going to give it a try.