The bulk of my suggestion may be found
here.
In thinking more about this, it is not a matter of file content, but one of file size that needs to be addressed.
Something like
- < 1 MB
- > 1MB < 8MB
- > 8MB < 75MB
- > 75MB
where each group may have a different number of active upload slots open. My options would be small numbers of large file uploads -> large numbers of small file uploads.