Ah, I forgot about Pacifist, thanks for the backup plan! Did you just right click on the 8 NVIDIA/GeForce extensions and select "Install Into Default Location"?
My current kexts (in 10.8.1 + Sept patch) are version 8.4.4 (304.00.00f20) & the ones in the 10.8.2 installer are 8.0.61 (295.30.20f02). I haven't had a chance to try the older 295 drivers since installing my GTX570 (1.28GB), so I might give the combo install a shot.
Edit: Oh, and jhero, have you had a chance to run Unigine in OSX? Sorry if you've posted it elsewhere, I'm just curious since I also have a 3,1 MP and am trying to gauge whether the GPU is even the bottleneck at this point. (Score: 1275, default, 1920x1200). Glad you got it figured out!
Roughly the same problem here (EVGA GTX570 2.5 GB version with no EFI mod), I'll try and give step by step of what I did. Sorry if it seems convoluted, just want to be thorough.
Had 10.8.1 running great with latest drivers from nVidia.
Ran 10.8.2 update, reboot OK.
Checked Uniheaven bench, CUDA-Z and Luxmark; the first showed a drop in FPS overall, the second showed that "memory copy" rate had dropped back to old speed previous to the nVidia retail-304 drivers. Finally Luxmark showed the no OpenCL device error.
Hexedit patched OpenCL framework, reboot and Luxmark OK with same performance as before.
Uniheaven still showed drop in FPS.
Looked in kernel extensions and saw OS X update had reinstalled vanilla drivers, tried to reinstall from nVidia retail-304 drivers download but it told me no update was needed. Checked OS X receipts plist and saw it still had reference to my previous install. Used Pacifist to force the reinstallation of the nVidia drivers, reboot to black screen on DVI2 and blinking grey screen on DVI1. Force reboot brings up an OS X dialog telling me it crashed and wether I want to reopen previous session or not. Neither work.
Reboot using shift key to safe boot, no signal to monitor, but with a bit of patience I can VNC into the login screen and to the desktop.
Manually overwrite Nvidia retail-304 drivers with 10.8.2 vanilla drivers, reboot no good, back to black screen.
Safe boot OK to login and then desktop.
Repair permissions with Disk Utility (GeForce drivers and OpenCL framework are the only modified files), reboot to black screen.
Download and install combo 10.8.2 update from apple.com (thank god for 100mbps Internet). Reboot OK but back to square 1; apply OpenCL hex patch OK and UniHeaven still shows performance drop. Performance measures were better under 10.8.1 using nVidia retail-304 & CUDA 5.0.24 drivers.
Guess it's back to 10.8.1 using TimeMachine (with ATI 5770 for boot screens) unless someone can confirm the performance drops noticed in bench apps are cosmetic, a fluke, or nVidia release a new driver soon.
edit: did my subjective test - loading a specific late game save from a big map in Civilization 5. I'ts been sluggish as hell except in 10.8.1 with retail-304 drivers where it was noticeably fast.