Stored Procedures are often written in a dialect of SQL (T-SQL for SQL Server, PL-SQL Oracle, and so on). That's because they add extra capabilities to SQL to make it more powerful. On the other hand, you have a ORM, let say NH that generates SQL.
the SQL statements generated by the ORM doesn't have the same speed or power of writing T-SQL Stored Procedures. Here is where the dilemma enters: Do I need super fast application tied to a SQL Database vendor, hard to maintain or Do I need to be flexible because I need to target to multiple databases and I prefer cutting development time by writing HQL queries than SQL ones?
Stored Procedure are faster than SQL statements because they are pre-compiled in the Database Engine, with execution plans cached. You can't do that in NH, but you have other alternatives, like using Cache Level 1 or 2.
Also, try to do bulk operations with NH. Stored Procedures works very well in those cases. You need to consider that SP talks to the database in a deeper level.
The choice may not be that obvious because all depends of the scenario you are working on.
https://stackoverflow.com/questions/5346601/stored-procedures-and-orms
