The excellent grayscale performance is needed, mainly because of Sony’s inexplicable decision to only include one adjustable color temp, which unfortunately corresponds to the brightest color temp. Usually, Sony provides the usual preset color temps (ie; D55, 65, 75 etc.), but then also provides custom color temps that use one of the presets as the starting point. Here, the adjustable color temp (Custom 5) is so low in red and so high in green that even maximum adjustments to the RGB gain and offset will not make to overall balance as good as the default D65 setting. Since there are already slightly less bright, but better color balance alternatives to the Game mode (Bright TV and Bright Cinema) that uses Custom 5, there’s no particular reason to adjust Custom 5.
Gamma settings allow for an overall gamma of 2.11 (with gamma set to Off or 2.2) or 2.30 (with gamma set to 2.4). Greyscale is slightly worse with gamma set to 2.4 as it increases red in the lower IREs, but not greatly. With both, the gamma curve starts at the target gamma at 20 IRE, then slowly drops as you move up the IRE scale.