You cannot fit more than four GTX 295 cards in any computer I’m aware of due to the double-width of the card. (However, each card has 2 GPUs on it which appear as separate devices.) Also keep in mind that due to the delays in rolling out Fermi, there is a major shortage of the GT200 GPUs used in the GTX 295, making them very hard to find in the retail channels. Waiting a month or two after the GTX 470/480 release might be a good approach. They won’t have the best bang-for-the-buck for single precision computations which scale well across multiple cards (in which case GTX 295 would be more cost effective), but at least they will be in stock.
If you are bandwidth limited, the newer cards will definitely have more bandwidth per GPU.
I would also stay away from water cooling due to the added complexity. There are no problems running 4 cards (the maximum you can sensibly fit in an oversized ATX case) if you have several large case fans. I have not yet had any problems with the four GTX 295 system I use with three 120mm case fans blowing over the cards.
If the problem that SPWorley mentions with the FT02 are not resolvable, the Antec 902 has 8 slots in the back, and thus room to hold four GTX 295 cards without blocking any slots. I have no experience with this case, but at least on paper it is the correct size.