expdp on a database with incremental stats enabled spends lot of time selecting from sys.wri$_optsta

The SQL looks like this while processing "Processing object type SCHEMA_EXPORT/STATISTICS/MARKER" path.

  SELECT intcol#, hashvalue
    FROM sys.wri$_optstat_synopsis$
   WHERE bo# = nnnnn AND group# = xxxxx
ORDER BY intcol#

I have incremental stats enabled due to heavy partitioning. The above table contains approx 70m+ rows and although it is partitioned on BO#, there are NO indexes on the table. Has anyone else experienced such slowness while expdp is processing SCHEMA_EXPORT/STATISTICS/MARKER path? I don't want to exclude stats but need this to be fast as well. I am sure perhaps an local index on (BO#,GROUP#) will help but I am not sure of that since it is a SYS owned object.