I don't have a lot to say here. Basically some tips and tricks. Basically: Yes, you can just throw a GTX 670 into your mac pro running 10.8 (or, I guess 10.7 with the NVidia drivers) and as soon as the login screen shows up, It Just Works. A couple of things: first off, I got the 2GB version, any more than 2GB and you have to hack the OpenCl drivers to use that feature in Adobe / Apple's apps that use GPU acceleration help. You can download the CUDA drivers off of NVidia's website but with Mountain Lion, you need *NO* additional drivers to boot and start using the card. I chose the 670 because it was Tom Hardware's "best card for the $$$" in that price range ($400). It is stupidly fast and has some extremely good cards out there. Which Model?: There are like 20 GTX 670's out there... kind of makes it complicated to decide. I've been using Toms Hardware guide for years to build PCs, so I relied heavily on this article and ultimately chose this card: So which one to choose? I chose the GIGABYTE GV-N670OC-2GD based on several reviews. This thing is One of the fastest cards because of an overclock chip (automatically overclocks when the card is cool... which it always is), but not the fastest (others can OC higher). It is also one of the quietest/coolest but not the quietest/coolest. I was basically looking for a balance between speed and temperature. Price is not a big factor because most of these cost about the same (unless they're the 4GB model). This model has 3 fans and is about 11 inches long--fits just fine in the Mac Pro, which tolerates even 12 inch cards. The thing really is amazingly quiet. Your Mac Pro fan will likely be louder. A couple caveats: Power: The stock GTX670 with two 6 pin power inputs will run perfectly off of the two 6 pin outlets on the motherboard, however most cards are not stock cards. Some GTX670's have an 8 pin plug which may require an adapter, but be careful as this will give the card the potential to damage your motherboard. However, provided you do not manually overclock the Gigabyte card mentioned above (automatic overclocking is fine), you will be well under the limitations of the computer (note: going over the limit is a bad idea). For other GTX 670's, check the reviews for power consumption information. [Edit: There is some trepidation about this, however as you can see in this post, the 5870 (shipped by Apple with the Mac Pro) uses more power than this card. GTX670 is particularly efficient. As long as you don't manually overclock the card, it will stay within reasonable amperage parameters even when using the automatic overclock chip. Other GTX670's with automatic overclocking may draw more wattage, so check the reviews first.] However, you need to buy a 6 pin to 8 pin adapter in order to do this. I chose to use my external PSU I rigged up for my second 6870 card. Why did I do this? Because I had it in place already and because I wanted to leave in a second video card for reasons below. Edit: Edit2: Later in this thread, "Redneck" suggests powering your 2nd card off a single 12v lead coming from the 5.25" bay. Please do not attempt this. I break it down here why that's a really bad idea. Boot Screens: No, you can't see boot screens with this... not until someone finds a firmware to flash it with. Personally, I like having the boot screen since I like to boot into windows a lot and use the boot selector (hold option while booting). Consequently, I have a second video card. Positioning: I keep it in slot 2 because I have two 16x PCIe ports in my Mac Pro 5,1. The 2nd slot has better ventilation and also I read on one of these forums that the behavior is better if you have your "primary" card in slot 1 in OS X. Second card issues: I have a flashed 6870 as my slot 1 card so I can see boot screens. Windows apparently has a huge problem running AMD and Nvidia cards at the same time... basically I uninstalled my catalyst (AMD) drivers and everything works great. However, the 6870 is probably not very useful for gaming now without those drivers installed. Basically, when I initially installed the 670, the screen remained black in Windows until I uninstalled the AMD drivers. I've had no issues in OS X. Technical issues summary: After arranging supplemental power and after fixing that windows issue, essentially I've had no issues!! I can't believe how well this thing is working. I have played BF 3 and L4D2 for many hours so far and it's working great!! I've also played SC2 in OSX, but didn't notice much speed improvement over the 5870 I was previously using, even though Barefeats.com says there's actually a huge step up. I imagine the Windows version of SC2 runs much better. Verdict If you have the means, DO IT. This setup is stable and fast as sin. If you require boot screens, you can get supplemental power from an external PSU that's not too hard to rig up, or you can get a GTX120 which requires no extra power (older macs can use a GT7300 or Radeon 2600).