The gauntlet has been thrown.
The ASUS GTX 680 DirectCU II TOP was made for overclocking, both the high-end heatsink and components used for energy distribution are proof of this. As such I managed to set the Core clock from 1137MHz (boosting to 1201MHz) up to 1214MHz (boosting to 1278MHz). That’s a 6% speed increase from factory settings and a massive 21% over reference Nvidia speeds. This was accompanied by a 86mV voltage increase to steady things up a bit.
Beyond 1214MHz it didn’t matter how much voltage I pushed, the card would crash. Of course, no production card is exactly the same, so your mileage may vary.