[Solved] Lots of updates to a large table. How to speed up?

by 


--Requete 40. Performance cost: 3%
UPDATE #temp_arbo_of_3
SET PxAchat=NULL, CuTpsAch=NULL
WHERE IdBE IS NULL;


--Requete 41. Performance cost: 2%
UPDATE #temp_arbo_of_3
SET CuTrait = NULL
WHERE IdBE IS NOT NULL;


--Requete 42. Performance cost: 2%
UPDATE #temp_arbo_of_3
SET NrOF_Source = _ofI
WHERE IdBE IS NOT NULL;

Now if I replace all this by:

--Requete 40. Performance cost: 3%
UPDATE #temp_arbo_of_3
SET PxAchat=CASE WHEN IdBE IS NULL THEN NULL ELSE PxAchat END,
     CuTpsAch=CASE WHEN IdBE IS NULL THEN NULL ELSE CuTpsAch END,
     CuTrait=CASE WHEN IdBE IS NOT NULL THEN NULL ELSE CuTrait END,
     NrOF_Source=CASE WHEN IdBE IS NOT NULL THEN _ofI ELSE NrOF_source END
WHERE IdBE IS NULL;

Performance (as indicated by SQL Server execution plan) is better. 3%+2%+2% > 3%

solved Lots of updates to a large table. How to speed up?