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True, the S5 image quality is the reason to buy the S5II, or S5IIX. When I review my 4K videos from my S5 on my 8K Samsung set, the image quality blows me away. On a different note, one thing I noticed about viewing videos on a 8K set (in my case 65"), you really notice the slightest changes in focus. Even when watching 4k high end movies on this set, I can see where they slightly missed focus. I would not have seen this as easy on a lower resolution set. I certainly would understand the comeback that 4k detail is still 4K detail on an 8K set. I agree, but somehow things just appear to be a tad sharper with more detail. You really start inspecting focus with pinpoint accuracy.
Not necessarily. When I was deciding which model to buy, I read reports of the Mark II producing images with less acuity and colour casts. It also lacks certain features that have not yet been implemented in the firmware. For a €900 saving, I went with the Mark I.