John,

I agree that there's only one column to be updated here and so it won't make much difference for this example, but using the strictly ANSI syntax for UPDATE in SQL Server will cause the execution time to double if you update 2 columns and triple if you update 3 columns.

As for the proprietary nature of SQL Server's UPDATE/FROM, do you really port code between different RDBMSs that often? It's just my opinion but, to me, true portability is an absolute myth because no one follows the ANSI standards 100% so might as well use the performance enriched proprietary features of each RDBMS.

Also, even with the good code you wrote, there's still the high probability of more than one cost being available for the scenario given so far.