One thing I discovered during the import is that the database table statistics need to be updated. The query planner was using the wrong index for this query of the convert application:
SELECT ipb_id FROM `convert_link` WHERE ( type IN('core_members') ) AND foreign_id='1667' AND app=1 ORDER BY link_id DESC
It was trying to use the "app" index and the query was taking around 3 seconds to execute. After updating table statistics by running ANALYZE TABLE against convert_link, it now runs in 0.0002 seconds.
Likely the statistics got behind because of all the data being inserted quickly.
