Looks like water cooling is the way to go. Expecting the cards and chassis to come in somewhere next week. Got a very detailed e-mail from EK with their products which also mention the full cover 7990's so will look into that and puzzle it together so the cards, chassis and hopefully the water cooling products arrive at the same time.
Also did put in a secondary PSU to make sure I do not run into power issues when the four 7990's are running at max speed.
Regarding the liquids to use, i see they have copper and nickel plates, any advice there what to use in combination with what liquid?
Distilled water all the way, some people add small amounts of 'wetter' which reduces the surface tension of the water. Not sure as to the benefits of nickel plating but mixing metals isn't the best idea when it's alu/copper cause you essentially turn the loop into a battery! Not sure what the consensus is on mixing nickel/copper (pretty much all radiators are copper). Secondary PSU is a very good idea too!