I've been hunting for an auto-tag solution for my collection. What tools are you using?
https://github.com/beetbox/beets
it takes a while to take a large library, but that's mostly because of intractable problems with ambiguity in metadata searching. I think it's about as fast as is reasonably possible.
Every new release that gets added to my collection will spend a few seconds in Meta so that I can check and edit the meta data and rename the files in a consistent way. Obviously you can also edit multiple releases at once.
I used quite a few tagging apps over the years, Meta is without a doubt the best of them.