I may have misspoke in an earlier comment. I've been testing the above code for ItemTestA with varying page sizes.

When page size is <= 64, there is not any noticeable issues with performance. Once the page size is 65, there is a 2 second delay between the SELECT statement being written to the log file and the Loader iterating the results. Once the page size reaches 180, the delay happens in the load getting the Result row for the last row. In this case, the delay is approximately 5 seconds.

As the page size grows, the delay happens at various points in the iteration by the Loader. The only constant observation is that as the page size increases, the delay increases but it is never at the same entity for different page sizes.

This is only under the case of the entity ItemTestA using the composite key. When doing the exact same tests with entity ItemTest, I can scale up to 2097 without any stalls. At 2098, the result set fails because of the SQL Server bind parameter limit of 2100.