The only thing 20W-50 will do is increase bearing heat with no benefit. With higher viscosity oil comes higher hydrodynamic friction and higher specific heat capacity meaning the oil will tend to run hotter and is more difficult to cool down. Higher viscosity also reduces additive response and solvency and increases the rate of air entrainment making it more prone to aeration. The 5W-40 is already overkill on viscosity and trending the wrong direction in terms of VII content, especially with Super Tech that uses OCP for VII.