>>
>>3. Instead of IF EXISTS INSERT I suggest to use MERGE command. It should be much better.
>>
>
>After having worked with it for years, I steer people away from MERGE in OLTP systems. It was really designed for, and is better suited for, ETL loads in data mart/data warehouse scenarios.
>
>But your original point is valid - it's best to optimize the IF EXISTS check.

Here is what Alexander Kuznetsov wrote about it

http://sqlblog.com/blogs/alexander_kuznetsov/archive/2010/01/12/t-sql-tuesday-002-patterns-that-do-not-work-as-expected.aspx