That's a very nice overclock for a socket 1366 processor. And a nice build.
However I'm not sure quad-crossfire 5870s is a good idea. Crossfire scaling for the 5800s (compared to the 5700s, the 6800s or the 6900s) isn't that great as I understand it. And with crossfire/SLI in general, the more cards you add the less improvement you get. The third 5870 will not be adding "much" over the first two, and I wonder whether the fourth 5870 is helping at all.
Actually, I just decided to look up some benchmarks. The quad 5870
sometimes does offer a benefit over tri 5870, and
sometimes does
nothing. I would be kind of interested to see whether CoD can use the 4th GPU or not.