I am running 2 x 6990 with the Haf x. I noticed that the lower gpu has way higher temperature compared to the top card. This is due to the hdd bays restricting the hot air venting into the case. We know that the design of 6990 pushes hot air out through both ends of the card, so all I can say is that 1 core of both your 2nd and 3rd card will experience high temperature. I would suggest removing the hdd cage to allow more room for the hot air to circulate but it requires drilling through the reverts holding the hdd drive bay. Anyway as a gauge the hottest core in my system is about 10 degrees hotter than the coolest core. In this case the core nearest to the hdd case vs the core nearest to the 5.25 inch drive bays. Overall Haf x is sufficient but I would suggest looking at Aerocool case http://www.aerocool.com.tw/index.php/products/chassis/28-pgsb/111-xpredator-black- if your budget permits and location sells them. The 4 x 120 mm fans on the side panel allows you to change fans depending on ur preference instead of the low rpm 200mm sidepanel fan of the Haf x.