Another set of interesting stats. When I run the queries minus the ORDER BY clause and select only the count(*) as with your conditions I get the following:

-- LEFT OUTER JOIN:CPU time = 27640 ms, elapsed time = 3694 ms.

-- EXCEPT:CPU time = 27566 ms, elapsed time = 3533 ms.

-- NOT EXISTS:CPU time = 25607 ms, elapsed time = 3280 ms.

Almost no difference. Why the huge increase in CPU time and reduction in elapsed time for the LOJ???

I've saved the query plans for all conditions and will look at them to see if anything jumps out.

I know this is way off topic now but I would like to pursue the subject. I haven't been on this forum for a long time. What's the best way forward? Is there a specific area for query plan analysis / performance tuning?