Address is a table with 400,000 records indexed on Addrnum
Cons is a table of 120,000 contacts indexed on CCust
Both have tags on DELETED()

The query...

SELECT A.* FROM Address A, Cons C ;
  WHERE C.CCust = "GREATLA2" ;
  AND C.PAddrnum = A.Addrnum ;
UNION SELECT A.* FROM Address A, Cons C ;
  WHERE C.CCust = "GREATLA2" ;
  AND C.Addrnum = A.Addrnum

runs about 50 times faster than...

SELECT A.* FROM Address A, Cons C ;
   WHERE C.CCust = "GREATLA2" ;
   AND (C.Addrnum = A.Addrnum OR C.PAddrnum = A.Addrnum)

Both queries show as fully optimized with SYS(3054,1), both return the same result set.
Strange uh!