I have dabbled with evaporative cooling. It works VERY WELL but it gets messy and condensation can be a big problem. It is one of the best ways to overclock though, short of liquid nitrogen.

Water cooling is something I profess limited experience with but I do understand the concepts. You will never be able to cool more than ambient as it only moves the heat from one place to another (the room).

You would have to cool 5 computers, 5 video cards and even then the benefits would be pretty minimal at best - you would be moving the heat from one place to another, and the CPU and the GPU are not the only sources of heat.... so I can't see that being viable unless you are water cooling outside or somewhere that was then chilled. Water cooling gets expensive with 5 rigs that need it though.

The heat needs to either go somewhere else, be cooled or not be produced at all. Not many other options really.