The BDC source here are in a MS SQL database. In most of the test the SharePoint indexing server, SharePoint SQL and the BDC data source SQL are in same server (a very powerful one). Initially the speed was very slow (7.5K per hour) and seems it didn”t downgrade as the crawled records accumulated all the [...]

Read the complete post at http://sharemypoint.wordpress.com/2007/12/12/load-testing-on-indexing-bdc-data/