INSERTS in REFERENCE PARTITION TABLES take twice as long as RANGE PARTITION TABLES

 I would like to use Reference Partition Tables but in Performance Testing I have noticed that doing Inserts into Reference Partition Tables take twice as long as doing inserts in Range Partition Tables.  My thoughts are that the additional time is required to determine the partition to insert the row into by looking up the primary key in the parent table.  I was wondering if anyone else has had this experience and if taking twice as long to insert a row is really the norm or if I should consider it an issue on the Exadata Oracle 11g RAC I am