Running a query over the network multiple times seems to choke performance, how can I pinpoint the problem?
You really need to generate an explain plan. Since your query has an OR there may be situations where the query is being short circuited based on data not existing, hence the performance is not consistent. Also, don't join everything together, subqueries with low cardinality put at the top in a WITH subquery_name clause, and join similar tables together, then join them with other tables.