Tara on "MySQL slow queries killing my site speed"

Have you tried deleting revisions in your DB? It may help reduce the DB size depending on the amount of revisions.

If you decide to do that, Make sure you backup everything (including your database) before doing any actions, just in case.

You can try the following SQL quiry:

DELETE a,b,c
FROM wp_posts a
LEFT JOIN wp_term_relationships b ON (a.ID = b.object_id)
LEFT JOIN wp_postmeta c ON (a.ID = c.post_id)
WHERE a.post_type = 'revision'

Note: make sure to change the table name in the above quiry if different than wp_