I have a slightly older Sony TV but the settings I've seen used over the years seem to be similar in regards to basic calibration. So yes, game mode will most likely have off all the post-processing effects and the default values for black level, contrast, and others should be fine.
The only setting that might need to change is the color temperature. Expert 1 is supposed to be the most accurate setting but if you're used to cool or neutral, it will be jarring for a few days. It will appear to have a yellow tint when watching bright whites but if you stick with it your eyes should get adjusted within a few days.
Make sure to turn on Auto Local Dimming so you can get deeper blacks and a better overall contrast. Just like the brightness setting, you can adjust this to your liking. High will give you the best contrast but this aggressive setting will cause blooming on dark scenes. I'd still use high though.
Every time I bring this up in the X800D thread, the defense force appears.