After you get better airflow you probably want to save those cards by flashing them with an optimized bios. There is a guy on the LTC forums named The Stilt that seems to be very talented at that. Here is the thread: https://litecointalk.org/index.php?topic=12369.0 all you need to do is search it for your card, download the optimized bios and flash each one. I guarantee that you will have much less heat produced by doing this one thing alone.

Just to give you an idea of what it will do, I also have a bunch of R9 280x sapphires. When I ran them stock the temps were like you said and the VRM (voltage regulators) were almost 120 degrees. After the Bios flash my VRMs run 65 degrees and the cards stay nice and cool at about 55-65 degrees. With 725Kh/s each..