I thought I left something out...
EVGA's GTX 680 for Mac has a reduced power need of only 195W versus the original's 550W. Would this be a benefit or a hindrance in a PC?
And the Mac version only supports PCIe 2.0. I imagine I would be limited to that through-put on a PC that supports PCIe 3.0.
The power usage I'm genuinely curious about. The PCI limitation (unless I'm missing something) I'm not hugely worried about.
And I have the answers, according to a rep for EVGA, maker of the GTX 680 for Mac:
In response to my initial question: The 680 Mac card will work in Windows in addition to the Mac OS.
In response to my questions about the power supply and the PCIe slots:
There are no issues when using the card in a PC, you would connect it just like you would normally. The card would operate as normal since the power in a PC is directly given to the graphics card as opposed as received through the motherboard for a MAC.
The card will work in PCI-e 2.0 and 3.0 slots.
It's not the most thorough response (as I asked if the Mac version would do the same job but with less overhead as the original and what through-put I'd get from the PCI slots) but they have confirmed twice that the card works just fine. So, apparently, when you pay the extra money for a Mac-ready card, you're also paying for backwards compatibility. Maybe that's a bit of a broad generalization, but it's true in this case.