Thanks for the thanks.
Five is the max you can get unless you go edit the fetch_similar_threads function in the /forum/includes/functions_search.php file and replace LIMIT 5 with LIMIT 10 (two spots inside the function) and then use $limit = 10; in the findtopic.php file.
Without the two edits to the fetch_similar_threads function in the functions_search.php file, $limit is good for zero to five. Anything less than zero would break the query, and without file edits anything over five gets ignored.