Well, the GTX 680 has the additional benefit that it is powered by just two 6-pin PCIE connectors.
What this means is that on the current Mac Pro models, you don't need any extra hacks for power, at least if you just have one card installed.
But I will state again what everybody has been saying one way or another: By the time Mac OS X has drivers for the card, I am willing to say that the reference GTX 680 model will be a "mid-range card" anyway. There will almost surely be over-clocked 680s available for purchase straight from some manufacturers. There will also be dual-GPU single cards that use the chip (GTX 690s?) and it may very well be that another Kepler GPU is introduced that is more power hungry but more powerful. Again, such a chip will probably use at least one 6-pin and one 8-pin PCIE connector and we will be back to where we are today as far as power connections are concerned. Especially if this new chip also powers the new generation of Quadros.
I will be completely impressed if Apple does the next three things at the same time:
1) Introduces a new
re-modeled Mac Pro
2) Such Mac Pro can accommodate more than one graphics card with a TDP of more than 200 watts with no hacking whatsoever
3) Drivers are provided so that the latest generation graphics cards at least boot on Mac OS X, doesn't matter if 2D/3D acceleration is not optimized.
Engineers that could solve all of these problems are instead working on the embedded graphics of the A6 processors and iOS. The amount of money that mobility devices generate for

just can't compare to the Mac Pro.