I was going to suggest @ITAngel
the same setup I have running in my 750D but it seems like there isn't enough space on the unused PCI slot covers to strap another 120mm fan from the inside.
Nonetheless, here it is, fans are all 1850rpm Gentle Typhoons which work the best in my senario
Top: 2 as intake nearer the front since the slot nearest the back as intake actually increases my CPU temps.
Front: 2 as intake
Bottom: 2 as intake, fiddling with temps suggests that it doesn't really do much. Maybe 1 degree difference in card temps
Top Back: 1 as exhaust
Bottom Back (Unused PCIE slots): Cable-tied a fan to the inside. This one made a huge difference to temps, a 5C drop. Since the case doesn't have a side panel fan to extract all the hot air thrown out by the card, this was the only other way.
Of course I did other mods to the card, CLU on die and Fujipoly Ultra Extreme on the VRMs.
Hope this helps. If not, you could probably ghetto rig a 120mm CLC to each die to bring down temps as well though it won't look as elegant