Hello David,
At this moment our test environment looks like this:
Content: 4 TB
DB: 4,9 GB
Lucene: 6,86 GB (11752 files, 3132 folders).
We have no performance issues with searching, though I must say that a lot of our content is image data.
Have you tried a full index rebuild? We have done it several times, and while it does take a long time (our server was unavailable for over 20 hours), it greatly reduces the size and file count of the Lucene indexes.
Kind regards,