Откуда данные о снижении быстродействия?

Если очень хочется - используйте свои процедуры для UPDATE.

P.S. BOL:
sp_executesql can be used instead of stored procedures to execute a Transact-SQL statement many times when the change in parameter values to the statement is the only variation. Because the Transact-SQL statement itself remains constant and only the parameter values change, the SQL Server query optimizer is likely to reuse the execution plan it generates for the first execution.

Note:
If object names in the statement string are not fully qualified, the execution plan is not reused.