I expect the primary advantage of 4k for most people will be the ability to scale 2x and retain a decent resolution. You don't save much (cost, battery life) by

I expect the primary advantage of 4k for most people will be the ability to scale 2x and retain a decent resolution. You don't save much (cost, battery life) by going to an intermediary size, but lose flexibility. On top of that, there are definitely noticeable improvements to be had significantly above 200 dpi.