I recently acquired a used EVGA 02G-P4-2684-KR and flashed it with the Mac ROM. So far it has worked as expected, the only thing unusual is that the boot screen from the HDMI output has a light green instead of the light gray background. Most issues and answers related to flashing the Mac ROM could be found from the following links:
1. EVGA announces a GTX 680 Mac Edition
2....
Confirmed and Possible Flashable GTX 680 Models
1. EVGA announces a GTX 680 Mac Edition
2....
Confirmed and Possible Flashable GTX 680 Models