We will have the 4U rack mount chassis in the shop soon. It will come with 7X high power delta fans, the fans are loud but have really high airflow and are very efficient at cooling. For testing purposes I switched them out for more quiet ones on the 8X 1060 GTX test rig, temps were around 55-63 before. Now with the quieter fans the temps are 65-72C.
https://www.youtube.com/watch?v=WEkYGOBeQcw