When running on windows there are a few quick tips that can help your file I/O performance.
You can exclude your package entirely from windows defender by following these instructions.
This gives significant speed improvements (~2x in some light testing), but also comes with some obvious security considerations.
By opting into this you are potentially opening yourself up to vulnerabilities.
Any Builder which is being applied to your package will no longer have its
outputs checked by Windows Defender. If you don't trust your (even transitive!)
dependencies then you should be wary of this option.
Note that the original package dependency sources are not in your package directory but instead in your pub cache, so they will still be processed by windows defender.
It is common for IDEs to run file watchers on your entire package in order to
update the file tree view among other things. Explicitly telling them to ignore
the .dart_tool directory and any directories that you commonly use with -o
can give a decent performance improvement.
In VsCode you can do this using the files.exclude option in your
preferences.
In Intellij you can right click on a directory, select Mark Directory as,
and choose Excluded.