The first thing is, don't use SELECT * type queries, ask for the columns you need only. For example:

SELECT ListID, Name FROM QODBC...Customer

The Advanced tab in QODBC Setup has defaults for Use Iterators and Iterator or Chunk Size fields. This allows you to turn off iterators. This may be needed on systems like MS-SQL Server and Web Servers that use multiple threads. Using Iterators is faster but is only available to USA QuickBooks 2006 and USA QuickBooks 2007 users.

Iterator or Chunk Size determines the size of the rowsets that are retrieved from QuickBooks. Set this value high if you are exporting records from QuickBooks. The maximun Iterator or Chunk size that can be set is 100000 (higher than that and it resets itself back to the default of 500). A good setting is either 10,000 or 20,000 if you have lots of data.