Чего-то я не понял, в новости говорится: "Примечательно, что в тесте с хранилищем из 10 млн записей PostgreSQL и MongoDB показали примерно одинаковые результаты."
А в оригинальной статье:
"The data(результаты тестирования то есть) is almost identical to the results found in testing with 10 million records. However, it’s important to note a Correction to earlier versions. PostgreSQL community member Alvaro Tortosa found that the MongoDB console does not allow for INSERT of documents > 4K. This led to truncation of the MongoDB size by approx. 25% of all records in the benchmark."

И вот выдержка из предыдущего тестирования (с 10 млн. записей):
"In testing, EDB has found that Postgres outperforms MongoDB in selecting, loading and inserting complex document data in key workloads:
  - Ingestion of high volumes of data was 2.2 times faster with Postgres
  - MongoDB consumed 35% more disk space
  - Data inserts took three times longer with MongoDB than Postgres
  - Data selection took almost three times as long with MongoDB than Postgres
"