哪个插入更快，XML字段或Varchar（max）字段？

We have a history table that stores xml web service requests and responses. Currently it stores them into an XML field, but we're having performance issues with inserts. We only insert records, no updates, selects or deletes. We've truncated the table and rebuilt the index, to no avail. The table has a Primary clustered index on the identity field, and a default value, GetDate(), on a datetime field. We're running SQL 2005 Server, but the database is in SQL 2000 compatibility mode.We have a history table that stores xml web ser