Closer than you might think. At 4K, the arc density is about a 14" VGA screen, which was totally usable. At 8K you approach a 24" HD monitor. That's ignoring the additional resolution you get from high refresh rates.

Here's an arc resolution chart I made: https://docs.google.com/spreadsheets/d/1pOx0Jcy6tpMGLxmPYX8n...