To be honest, the Sun intensity value is too high.  If you are using Superfly rendering and relying on HDRI illumination as well as an infinite light, I would reduce the sun intensity value.  Whenever I create an outdoor scene with a combination of HDRI and physical lights, the intensity value of the lights are decreased tremendously.  I have used values of 50% or lower, depending on how much of an influence I want the HDRI to impact the scene.