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More serious samples in natural light (or nice level of its absence) - GH5s and Terra 4k
 

How to catch balloon in the dark
 
 

Yeah you can use a speedbooster with them. The XH1 120fps is not as good as the XT3's. 

I'd consider the Nikon Z6 it has very nice 120p. I'd say the Nikon Z6, A7III, and Fuji XT3 have the nicest 120p on the market right now. The Pocket has great 120p though its cropped 2.8x 

The Nikon is a good option. Though if you already have M43 lenses a Pocket 4k would be an easier switch. Just be ready to use NR in post for a clean image at high ISO's. 

Not yet. But it seems like external recording looks great on this camera (basically unprocessed and really smooth). Will rent it in the near future for sure.
Also consider the Pocket 4K.
Add a speedbooster XL and it will shoot at a 1.2 crop.
If properly exposed even ISO12800 still looks really nice.
When recording RAW it is basically unprocessed footage - something you can only get from way more expensive cameras.

Maybe to include as variable relevant to question: exploring choice of appropriate lenses? 

Do you need 10 bit? Fuji has nicer color science but the A7III ain't bad, HLG looks pretty nice. When comparing the cameras they'll all capture roughly the same amount of detail on these settings; GH5 3200, XT3 6400, A7III 25,000