One client send me his content to fix an error and I got website with more than 4.000 pages. That is quite a lot. The frontend website was still very fast, but the backend website was a bit slow. Publishing, unpublishing or deleting pages took more than one second. I was a bit shocked, because it was not the cms that I loved for its simplicity and performance anymore.
The reason behind this: Typemill uses a hierarchical navigation with all pages that is always visible and accessible. If you change one page, then you have to regenerate and cache the whole navigation, similar to a static website generator.
The solution worked quite well: I seperated the navigation for each content folder, so you only have to recreate the static navigation of the folder. This improved the speed for actions like publishing or unpublishing from 1 second to about 0.1 or 0.2 second.
There is much room for more performance improvements, but at the end Typemill is simply not build for large scale websites. I created Typemill for documentations and similar web-projects, so I think you can use Typemill now for websites between 5.000 and 10.000 pages.
Read more about the release here: https://typemill.net/news/typemill-2-4-0-seo-performance-and-cyanine