Now you can find the same 4K video from few GBs to a hundred GBs, and I am wondering: where to stop? With music there is a similar phenomenon by which after a certain bitrate it becomes an esoteric art to detect improvements. So, what is your “very good enough” bitrate for 4K videos?
That is too broad of a question for a too narrow of an answer. You can answer with broad statements and generalized estimations, but I don’t think they really answer the question.
Encoding video balances three things (extensible by two more):
The codec you use also has a high impact on compression ratio opportunities and capabilities. AV1, HEVC, AVC? 10-bit?
If we define that we do not care about encoding time, so we will use the very slow preset and use all codec features available, compression ratio and quality falloff still depends a lot on what you actually encode.
I suspect in higher resolutions the gaps between different visual data compression ratio differs more - because a difference is elevated through higher resolution/more data.
That being said, I don’t have or use 4K stuff, so I can’t even check for some rough numbers and visual content to size differences.