Pixels Per Unit and supporting large (4k) resolutions

I'm trying to decide what PPU I should use for my standard 2D tiles.

As far as I know, it makes sense to create art assets in as big a res as you can, and then save the pngs at a smaller res. For example, if I save a tile at 256x256, I should get a tile that's around 1/8 the height of the screen on a 4k display, correct?

In order to avoid upscaling, does that mean my camera's orthographic size should be 4 and my PPU should be 256? The screen would be around 8 units tall and a 4k screen can fit around 8 256x256 blocks without upscaling. I'm just confused about how to do this (and test it) because I'm developing on a 1080p monitor.

I also don't know if there are any major performance downsides to using large sprites when most players will probably end up downscaling to 1080p anyway. I'm not targeting mobile; just PC and hopefully console.

To summarize: am I correct in thinking that I should save my tiles at 256x256 if I want them to be about 1/8 of the screen and still look good on a large display? And is 4 a reasonable camera size in terms of Unity physics?