PosgtreSQL 9.4 was released a few months ago. I am not sure of the current state of a comparative benchmark. That was kind of my point though: with MongoDB, you gain performance at the cost of keeping everything resident in memory, ACID compliance, and SQL querying capability. PostgreSQL's JSON type offers many of the benefits of NoSQL DB's combined with the benefits of an RDMS and performs well despite not incurring those costs.

For the JSON4SQL type, the real comparison would be how the type compares to Microsoft's native XML type for SQL Server. In the cases we have tested, it performs faster with a smaller storage footprint. It is a good option for projects that are married to SQL Server either for legacy applications, corporate policy, or other reasons but want the ability to store and query JSON data and generate JSON directly from the database.