Please check what graphics card are used in these 6 GPU rigs. They are using GTX 1060, 1070 or 1080.
There graphics cards are considerably cheaper and have much lower performance.
We are only using top of the line GTX 1080 Ti graphics cars; they are the fastest Nvidia cards on the market.
Only GTX 1080 Ti GPUs can give you the best profit and hash rate.
This way our 3 GPU mining rig can give you the same or even better hash rate than 6 GPU rigs on cheaper cards. Please note that these 6 GPU rigs will occupy more space, emit more heat and are more difficult to setup and maintain.