>I'll try later - busy with work right now. I tried on the tables I had in my test database (in SQL Server).

Ok I just tried for you:

                              t6   t5   t4   t3   t2   t1
Client processing time         0    0    0    0    0   16 
Total execution time        2328 2296 3046 2250 2328 5937 
Wait time on server replies 2328 2296 3046 2250 2328 5921 

Two passes. t1,4 (LEFT), t2,5 (NOT IN), t3, 6 (Exists).
Cetin