In violation of the suggestion in this thread to keep extraneous files out, I’m also attempting to run Obsidian in my Dropbox root folder. However, unlike the tests here of vaults with lots of notes, my situation is that my number of markdown files is not so large (between 400 and 2000 at the moment, depending on whether I remove some checked out source trees), but there are very many “attachments” (11,000 PDFs, 130,000 PNGs, and, generally, half a million files of any kind).
Since [[ auto-complete includes attachments, it is slow and includes uselessly many results. Also, startup takes a few minutes, but is bearable. However, I don’t have problems browsing the file tree, and following links is instant.
In fact, it’s actually very close to being usable in this folder, and, if @johw’s suggestion of restricting search to markdown files was used (likely in a few key hot spots), it would probably be solved.