Are you running any scaling on 5K 27 or 32 6K?

I have 20/20 vision and a pretty normal desk setup. I run my 32 4K at 100% scaling in Windows, and while I could maybe push it down a little smaller, some of the least PPI-aware interfaces and text would start to be too small.

If you're running 6K scaled to 150%, you basically just have a slightly sharper 4K monitor - effectively 0 extra space. If you're not running it scaled, I'm betting you're sitting closer to the monitor than is recommended for long term use (or have like 20/10 vision).