The pureXML technology in DB2 9 only parses XML documents at insert time so that they are stored and queried in a parsed format. This is denoted in DB2 9 by the use of the new XML data type. The parsed format is a tree structure of nodes as explained in page 2 "XML document tree storage".
XML documents can be stored in CLOB columns. They are inserted as unparsed text objects. No XML parsing at insert time can be a performance benefit, especially in CPU-bound systems.
On the right pane, click the buttons in order to obtain an average insert times for XML data in XML columns and CLOB columns. Theoretically you should see CLOB inserts is faster than XML inserts. However you may see the opposite in this sample due to insufficient amount of data.