QSqlQuery vs. SOCI: inserting 1000 times

Recently I'm using QtWebApp to develop an application, and I did some performance benchmark to select a database library in the backend.  I selected QSqlQuery and SOCI as candidates, and tried to insert 10,000 rows at once. The result is as follows:

• Repeating single query
• QSqlQuery: 10000ms
• SOCI: 2500ms
• Prepared statement
•  QSqlQuery: 7000ms
• SOCI: 750ms(?!)

In any situation, SOCI takes far less time than QSqlQuery. QSqlQuery seems to be really a bad choice for server applications. I suspect the bottleneck is the loooooong processing time for QString.