If I understood this correctly, looks like the stock fans are doing a good jobThere you go:
View: https://www.youtube.com/watch?v=IYsOmJ9X7Ow
Or you can read it:
https://www.gamersnexus.net/hwreviews/3624-corsair-4000d-airflow-case-review-vs-solid-panel
Far as I remember whatever benchmark it has "stock" after the case name, it means stock fans, in its factory position.