I want to spend as little as possible
Since the cards are currently watered I'd suspect I'll go with water and turn my current WC gamer into an airbreather. I'm thinking the main determining factor is more space for the board and the cards moreso than the cooling solution. I have a Koolance dual bay resv/pump that fits into two bay slots so that really isn't a concern.
Maybe I'll use my Corsair 800D and put the air breather into a HAF of some sort?
I'm thinking I'll go Tri Sli too instead of Quad Sli, make the spacing issue a little easier to accommodate