Thanks for your answer.
Here were I live is not so easy to rent exactly that kind of devices.
As I said, my field of study orients me toward video-art. Video-art means all and nothing, but we can clumsily say all that kind of video installations you can find in a modern art gallery: from Nam June Paik to Bill Viola, Stan Brackhage, pixel art, generative video synthesis, 3D animation and so on. As I said: all and nothing. What do I plan to do? Well, I'm going to start on two fronts: on one side
SHARUNAS_BARTAS' style, and on the other side
TACHIGUISHI-RETSUDEN's style, so natural-light hieratic documentary language on one hand, and stills-based animation and compositing on the other hand. So I need a camera for stills and video: stills for animation and compositing, and video for natural-light-docu style.
Said this, both kinds of file will require a lot of post: cropping/filtering/keying/rotoscoping for stills, and grading for videos.
As you can see, both stills and videos require ideally as many bits as possible... in a reasonable compromise, of course!
Reasonable compromise - for me - means working in a practical way, so the least rigging as possible (as I'm a one-man-crew).
What is my ideal camera? A practical little cam that can do big stills (to crop in post), can handle natural-light without problems, can do videos with good bits for grading. Simply it doesn't exist. But compromises do exist. I'm only trying to understand which is the best one for me. For example: A7S is a tiny cam, it's good for every amount of light (expecially A7SII), but for stills-to-crop-in-post A7RII is better, and for bitdepth BMCC is the king. If GH4 had better managed low-light, I would have considered it as the best compromise (tiny cam, 16MP stills, 10bit) but it lacks just a big feature: low light. A camera that forces a one-man-crew to bring lights and reflectors with him, that gives its best only in specific conditions, only when the sun shines, only with fast-fast lenses+adapter at widest&softest aperture that means no-damned stabilization that implies a tripod... well, this "smart" cam lacks another big features: it's not a practical cam at all!
In this compromises match, Sony seems to be a good solution (A7RII or A7SII), but lacks 10bit, and this is not good at all thinking that I will surely heavely grade in post.
If you say, guys, that 8bit or 10bit from GH4 is not a big difference for grading purpose, then simply I will go for the Sony.
This was the meaning of the question of my last post: what does a color artist think could give a better result with grading: dark&noisy 10bit GH4 evening footage, or clean&clear 8bit A7S evening footage? (Please, let's image to be that color artist, and to have this couple of evening takes, and simply try to anticipate which take will work better.)
Thanks a lot for your patience.