You might be on to something.
http://img846.imageshack.us/img846/5624/p1040777.jpg
I didn't make it an inline photo because it is kinda big. My GPU temps tend to be ~45C at 100% load overclocked to 920.
I want to try 4x but I need to find a MB which has this slot configuration
16x
something
16x
something
16x
something
16x
There are some AMD board with that layout but I haven't seen an Intel ones (at least not ones that cost less than $300). I also need a different case (one which has 8 expansion slots to fit the 2nd half of bottom card).
Please excuse the crappy wiring job. Still haven't got around to wiring it all nice (power button not even hooked up yet). I might write up a "guide" about what I learned setting this up.
Just got that power supply. Enermax MAXREVO. A 1350W super efficient beast!
If you want the cheapest possible rig price nothing beats air cooling but if you want density, a case you can actually close, and nearly silent operation well the only option is water cooling.