71-72c is not hot for a GPU.
What are CPU temps?
Have you optimized the airflow in your PC-9F?
If you need a bigger case with great airflow, I suggest you give the Phanteks Enthoo Primo a look. Great case, comes with 5x 140mm fans, is cheaper, great customer support, and a great club thread here on forum.
Another great case is the Fractal Design Define...