Then spend some extra bucks with the following items:
That's because the external PSU is not synchronized with your internal PSU, you have to turn it off manually. The molex plug is supposed to put these two PSUs in sync.
This could be a problem for System Profiler recognizing VRAM greater than 4GB or an ATI driver issue. Check if the applications you intend to use could recognize all the VRAM. After all that's what really matters, not how it looks in the Finder. If you have access to 10.8.4 beta, you could try it since it can properly display 6GB VRAM of the Titan GPU.
It seems this is more likely a driver issue until AMD could fix it. There is something called "OpenGL Driver Monitor" which is part of the Apple Developer Tool, and it could be used to track the GPU VRAM usage as explained here. See if you can get hold of a copy and help you with the VRAM usage.
I don't believe there would be any problems as long as you got enough power for both of them. BTW, you should find a way to let AMD and Apple know the driver issue, and hopefully they'd fix it before 10.8.4 comes out. NVIDIA seems to do a much better job on the Mac side.
(I trusted the earlier poster who swore that there is nothing wrong with just hooking in the 7970 to the Mac Pro and let her go. Yes, it works but when I am loading my graphics card with Aperture or Final Cut, the whole system shuts down cold. I mean immediate black screen, hard reboot. Without warning. Clearly the power draw goes up and the system kicks out on some kind of safety preservation mode. Thank God. Perhaps he has a higher tolerance for some reason but I have three other graphics cards and it doesn't ever do this. So, against the advice of many here, I listened to the experience of one and now I see he is wrong. I will try to figure out what power supply I need to hook up to make this thing work. On top of all that, it never made a lick of difference in any of the Apple Apps I use. FCPX and Aperture mainly.
I trusted the earlier poster who swore that there is nothing wrong with just hooking in the 7970 to the Mac Pro and let her go. Yes, it works but when I am loading my graphics card with Aperture or Final Cut, the whole system shuts down cold. I mean immediate black screen, hard reboot. Without warning. Clearly the power draw goes up and the system kicks out on some kind of safety preservation mode. Thank God. Perhaps he has a higher tolerance for some reason but I have three other graphics cards and it doesn't ever do this. So, against the advice of many here, I listened to the experience of one and now I see he is wrong. I will try to figure out what power supply I need to hook up to make this thing work. On top of all that, it never made a lick of difference in any of the Apple Apps I use. FCPX and Aperture mainly.
