Here are two screen capture of the LX100 shot with ISO800:
The Octopus is night dive, while the Nudibracnch is day time with custom white balance without video light. As you can see ISO800 on the LX100 is usable and pretty good, just not on scene where you have lot of blue color water. The Sipadan LX100 clip posted at the top of this discussion shows very nice/clean blue, I'm not sure if it's because the diving condition in Sipadan is much better than Anilao, or the fact that the Sipadan clip is 1080 instead of 4K sort of hide the noise at the blue part of the clip.
I'm still going through my clips, I have about 800 clips! If I found some that show the water column in ISO400 or ISO200, I will post it here for people to judge/reference.