Magnus rotors are efficient with both a high spin ratio (2 to 4) and a low wind speed, avoiding a too high tangential speed which increases by the cube. A high wind speed and a high spin ratio lead to a huge power consumption overcoming the delivered power. A spin ratio of 4 with 15 m/s wind speed is to forget. It is a reason why Magnus rotors are not massively developed.
From theory and also some experiments I made, the Sharp rotor is probably better for AWE at least for high winds.