All air cooled. Here is my current layout (I just reconfiged the boxes to get 4 gpu engines (3 cards) into Red Dragon).
Blackdragon
GPU Brand Voltage Power Limit Core Clock Memory Clock Fan Speed Temp C Gigabyte GV-R797OC-3GD 1168 +20 1200 1500 auto 67 Gigabyte GV-R928XOC-3GD REV2 stock (1200) +20 1200 1500 auto 63 MSI R7970 Lightning 1175 +20 1200 1500 auto 59 (right above bottom case fans)
Red Dragon
GPU Brand Voltage Power Limit Core Clock Memory Clock Fan Speed Temp C Gigabyte GV-R928XOC-3GD REV2 stock (1200) +20 1200 1500 auto 72 Gigabyte GV-R928XOC-3GD REV2 stock (1094??) +20 1200 1500 auto 65 XFX FX-799A-6NF9 HD 7990 gpu1 stock (1165) +20 1200 1500 auto 74 2nd 7990 gpu (one 7990 card total) stock (1135) +20 1200 1500 auto 62 This side of card above bottom fans
Each case has 3 graphics cards, the lower card are mounted in the lower power supply hole and tied in place. The bottom cards are attached by PCI-E extenders. This allows me to have extra space between the cards. Using Sabertooth slots 1, 4 and 6 a.k.a. PCIe 2.0x16_1, X16_3 and 16_4.
I rearranged a lot in the cases to keep air flowing. Modified the Cool Master HAF 932 side panels to include 200mm fans (cut through the plastic of one panel and added fan grill, replaced the panel on the other). Power supplies are mounted at the top back of the cases, exhausting out the back. Put 2 120 mm fans in the bottom of each case. Mounted the Corsair Hydro Series H100 to exhaust out the top front bays. Change the default case fans; adding high flow 140mm out the back and 200mm intake fan in the lower drive bay. Added 200 mm fan on top of each case, pulling air out; these are external mounted with fan grills on top (they don't quite fit in the case with the PSU at the top). So 4 intake fans in bottom half of the case and 4 exhaust on the top (not including the PSU, count 2 for the H100). I can upload picks if desired. These boxes ended up this way back when I was running Donate as hard as possible and Donate generated the most heat on the 7970s.
Red Dragon pulls too much power for the Antec 1000 mounted in the pc, the power to the bottom 2 cards is supplied by an extra Antec 1200 that has 3V issues, but good 12V rails. I used Add2PSU Multiple Power Supply Adapter to control the power supplies together (too lazy to hot wire it myself). Handy setup, because I can split the PSUs across 2 UPSes.