Update statistics causing negative performance

Recently we have seen a negative performance for a query that is running against a 500GB size of database, where AUTO UPDATE STATISTICS is enabled and we perform weekly reindexing on this database. In addition to this I perform intermittent update statistics against set of tables that has frequently update/deletes. As usual I have checked for TEMPDB contention during this query operation, nothing found wrong. Event Transacton log backup is continuing very well. Then realized that this could be a...(<a href="http://sqlserver-qa.net/blogs/perftune/archive/2007/08/17/1491.aspx">read more</a>)<img src="http://sqlserver-qa.net/aggbug.aspx?PostID=1491" width="1" height="1">