Yes, Except seems like the hardest of the join operators for the query engine. Wouldn't the two-way compare

SELECT * FROM

(

SELECT * FROM Staging.dbo.WIDGET

EXCEPT

SELECT * FROM Production.dbo.WIDGET

) LEFT_DIFFS

UNION

SELECT * FROM

(

SELECT * FROM Production.dbo.WIDGET

EXCEPT

SELECT * FROM Staging.dbo.WIDGET

) RIGHT_DIFFS

Work better as

SELECT * FROM

(

SELECT * FROM Staging.dbo.WIDGET

UNION ALL

SELECT * FROM Production.dbo.WIDGET

) BOTH_SETS

EXCEPT

SELECT * FROM

(

SELECT * FROM Production.dbo.WIDGET

INTERSECTION

SELECT * FROM Staging.dbo.WIDGET

) INTSCT