I think that if you want the most out of a RDBMS, then ORM is never the way to go. The problem being that objects and database rows are not the same thing. Not even a little bit. If you squeeze that square peg through that round hole, you shave off 80% of the point in doing so. Object Relational Mapping is basically a contradiction.

If you are only using the subset where the cost of using an ORM is negligible, you're probably not really using the RDBMS to its full extent and maybe you should consider a document oriented database instead. Relational databases are stupidly powerful if you let them do their thing. Kind of a pity to reduce them to a k/v store.

That said, there's totally a segment of CRUD:y non-performance-critical applications where ORM is a non-terrible choice.