Like I said before, I have almost the same build with exception of the case and PSU which shouldn't make a difference. I was having the same frustrating problem. Out of desperation I reformatted my HD and installed 10.8.2 again. I used the latest version of MultiBeast 5.1.3-1 checked the NVIDIA Fermi>2GB OpenCL Patch and all the other suggested fields and restarted.
The only thing I did different was I didn't install the latest NVIDIA driver, I just left the one that was installed with the ML 10.8.2 install. I plugged in my GTX 570 and restarted and "bam" it worked. I think there is a problem with the latest NVIDIA driver. I don't know if this helps, just thought I'd let you know.
