Regarding 2k 4k and bit depth etc.. let me put somethings together for easy understanding of the very subject. I am not going into nuances of micro things like camera sensors and compressions log, linear, projections, human eye perception etc…, as those things would make things even more complicated, lets keep it basic and primary for this discussion.
Resolution: Resolution is equal to Size
Lets take examples of photograph sizes and relate it for understanding.
2”x4” is 2k
4”x8” is 4k
8”x16 is 6k
What happens here is, bigger the size of photograph happens to be your resolution. So when we talk resolution it is effectively the size in terms of pixels. Which eventually resolves to the fact that we see more details as we enlarge. But if we go beyond the acquired sensor resolution we won’t achieve anything (upscaling) even down scaling would result in losses.
“Lets take 4 gallon container of water and we have to use only 2 gallons of water out of it, what happens to balance 2 gallons ? you have the answer to yourself :)"
Bit Depth: Bit Depth is Quantity
While bit depth is variable and that is the biggest and most expensive thing to acquire since it takes disk space and makes the file heavy. We get more tonal range as the bit depth starts going higher, and that’s what we at times refer to in most of our discussions “is there enough range in the image”.
When we see a good image which is has more tonal ranges we love it, while the one with less amount of tonal range seems very weak. Even if the image is small in resolution and has more color bits we love to see those beautiful tones and that what’s makes the big difference.
Bit Depths is independent of resolution, even a .5k file having higher bit depth would look amazing, so imagine 16bits of colours projected in 8K.
Now to get back on the very discussion, having even a 2K image with maximum bit depth for projection is absolutely great, but again we are greedy creatures, why not 4K at 10bits.
here is an interesting simple to understand link from wiki.