The airplane with the higher stall speed has been used as a test airplane. The stall is aft stick limited. I have eliminated the horizontal tail and elevator authority, it is sufficient to get it stalled properly. I tried different angles of stall strips, that did not change stall speed. It is a single engine, piston. Adding a small amount of manifold pressure as opposed to throttle fully closed decreases stall speed by several knots. The wing leading edge contour was slightly different from the other airplane, we tried to rework it to match, that reduced stall speed slightly, but not enough.