ISO 50 and 100...?
I think this is what people mean when they advise against using "lower" ISO settings. If your camera has a base ISO of 200 for Raw, but can be "extended" to 100 for JPEG, the camera is essentially overexposing by a stop then pulling the exposure back in JPEG processing. The problem is that the initial overexposure can lead to diminished highlight headroom or completely blown out highlights. If your camera's actual base ISO is 100 or 50, though, you'll get the best results there.