Thanks for the tips, and in particular:

Iustin Pop wrote:

  - if you download torrents, fragmentation is a real problem, so use a
    filesystem that knows how to preallocate space (XFS and maybe ext4;
    for XFS use xfs_io to set a bigger extend size for where you
    download)

That's a very interesting idea; it also gives me an opportunity to 
experiment with XFS. I had been avoiding it because of possible 
power-failure issues on writes.

-- 
Moshe Yudkowsky * moshe@pobox.com * www.pobox.com/~moshe
  "She will have fun who knows when to work
   and when not to work."
    			-- Segami