The GeForce GTX 680 can easily be flashed to become the GTX 770 by using a custom BIOS from the GTX 770 board, here’s what the user had to say:
The upcoming GTX 770 is a GTX 680 in disguise. NVIDIA has gently revised the GK104 architecture, mostly with process improvements, but the 770 is basically the same beast! Which is good for us enthusiasts.
By flashing the included BIOS (.bin) to your board, then dropping the included .inf file into the 320.00 driver package before installation… you too can have a GTX 770 weeks before it’s released! Please note it has to be a 320.xx driver, as support for the 700 Series was added in the DLLs around this time.