Gigabyte GV-N680WF3-2GD has made it into my Mac Pro 3,1 (2008) -thank you, Santa!
It is basically your stock NVIDIA 680, but with 3 fans, and without over clocking. Hopefully, it will be quiet.
The box contained two cables:
1) two 4-pin molex to a 6-pin, and
2) two 4-pin molex to an 8-pin.
The second cable had
only 6 out 8 pins actually populated. I wonder why Gigabyte bothered with an 8-pin in the first place... compatibility? I filed a question with their tech support - no response so far. I used it anyway(for now), but I am vary tempted to switch to a 6-to-8 cable and take the power directly from the motherboard.
Experience with the stock drivers:
I am running 10.8.2 so the card was instantly recognized, but it would only operate two monitors: DisplayPort and one DVI.
It is possible that in your scenario it will handle 2 DVI ports - I have to use a DVI-to-VGS adapter on my second DVI port, it might interfere somehow.
When I plug the HDMI cable into anything, there is a blip on all monitors like the OS has noticed an event, but the new display is NOT recognized.
Experience with NVIDIA 304.00.05f02 drivers:
Four monitors are up and running beautifully (yes, I need five, but that's another story). There is only one hiccup: It would appear that the HDMI device recognition is borked. I cannot tell yet whether it's a driver problem, a card design issue, or an actual fault.
Basically, if the HDMI cable is plugged into ANYTHING at boot, the system hangs. Same happens when it tries to wake up from sleep. If I boot the computer and THEN plug the cable into a monitor, everything works perfectly.
If you have run into smth similar ( or enjoy a perfectly working HDMI on Mac Pro 3.1 with a 680) - I would love to know.
I'll keep digging. meanwhile, if the community wants to know anything - I have no problem posting a few screen shots