Just installed a PNY Quadro P600 in my Mac Pro 2010, and using the latest Nvidia web drivers on Sierra. The only thing missing is the Apple boot screen (that I can tell) but everything works flawlessly. And the card is so much smaller than the original Radeon 5770, it's almost like 25% of the previous volume. This is the most affordable Nvidia Pascal card that will give you 4 DisplayPort outputs in a single slot. (Got it for just under $300 CDN on Amazon.)
Two notes when swapping out the card:
- Remember to move the fan back into position afterwards (this engages the locking bar at the bottom of the card), otherwise you'll hear buzzing and vibrating.
- When reinstalling the backplate hold-down bar with the two spring-loaded screws, be sure that one end slides under the small tab, otherwise the card backplates won't be held down properly. If you want better stability, you can still use individual screws, but be careful not to drop them inside the Mac.