Some people have used 5K displays at 4K without even knowing it. I guess if you don't know how good 5K can look, then the fugliness won't matter?I heard that running your 4K upscaled on a 5K monitor looks fugly.
Certainly option 3: 5K scaled down to 4K then scaled up to 5K cannot be as good as option 2: 5K scaled down to 4k. But maybe you won't notice it. At least it should appear better than option 1: 1440p?