Hey iMac 4850 owners. It's avihappy again and I have another survey for you all. As you can see, there is now an iMac 4850 EFI firmware update available via software update. So can you: Find a test that will cause the iMac to freeze up. Do the update. (make sure you actually run the firmware updater tool, it may not run automatically when you install the update from Software Update.) Switch to WiFi. Do the test again. See if the iMac freezes!