Re: Restarted my machine, now suddenly NOTHING works with my GTX670?
Ok looking at your xorg.conf a little better, Xinerama is disabled (good), you have three displays configured for TwinView (that's good for them). You should be able to just comment out that line at the end that disables compositing. Then log out, log back in and try running compiz.
You should be able to add the fourth monitor to your TwinView setup.