This post is currently a work in progress. I want to understand the correct procedure for installing the Nvidia web drivers with a non-EFI (un-flashed) Nvidia Maxwell card in a cMP and also the correct procedure for updating OS X. I'll update these steps as others correct my mistakes. This is what I've gleaned so far... NB: These steps assume you have a spare EFI stock Apple GFX card to use i.e. the GT120. I don’t use boot camp or windows and don’t game, so this info may be missing some important points on that score. Also, as pointed out, there can be no single set of steps that cover all eventualities. Non-EFI Maxwell card - initial driver & card installation procedure: 1. Find your OS X build in ‘About This Mac’, discover the correct corresponding Nvidia web driver via this really useful page at Macvidcards and download/install first. 2. Open the newly installed System Preferences>Nvidia Driver Manager and switch to ’Nvidia web driver’. Shut down. 2. Install the card into your Mac Pro. 3. Reboot. Non-EFI Maxwell card - OS X update procedure: A few days after an OS X update arrives the updated Nvidia drivers are released. You must wait for these before updating OS X. 1. Install your GT120 or equivalent EFI card into a spare slot and plug a display into it. 2. In System Preferences>Nvidia Driver Manager, switch back to ‘Default OS X Driver’. 3. Reboot. 4. Install OS X update via App Store and reboot. 5. Locate and install the correct Nvidia web driver. 6. Switch back to ’Nvidia web driver’ via System Preferences>Nvidia Driver Manager. 7. Reboot. Other points of note: - EFI stands for Extensible Firmware Interface. Learn more about it here and here. PC versions of Maxwell GFX cards do not contain an EFI (they have a BIOS instead) and therefore will not display a boot screen on your Mac. - Although the speed difference between PCIe 1.1 and 2.0 is negligible, it’s worth knowing that the Nvidia web drivers allow the card to connect at 5.0GT/s PCIe 2.0. - The same OS X versions can come with different build numbers. It's important that you match the correct Nvidia web driver number and OS X build number. - I’ve read other users having issues connecting a 6 pin to 6 pin cable to the 8 pin connection on cards like the 980ti. One solution to this is to obtain an 8pin to 6 pin PCIe power cable. Please feel free to correct any mistakes or add any omissions and I'll update accordingly. Thanks.