The temperatures would be atrocious. These things are already hot, now four of them in one setting?
Even with liquid cooling..... a GTX480 from HardwareLabs (hehe, just realized the names match) can do what, 1600watts of dissipation at ten degrees delta T, with fans at 2600rpm? And the Fermi cards are hotter than the 5870, so the 5870 had what, 500 watts to dissipate at full load?
You need dual quad rads to keep 4 GF100 cards at decent temps then. With screaming fast fans.
Wow, just wow.