Over on Reddit a user claims that a simple BIOS flash of the GeForce GTX 680 could turn it into a GeForce GTX 770. The BIOS probably works all reference-design GTX 680 boards, along with a GPU-Z screenshot of a "GeForce GTX 770" obtained this way. The BIOS runs the card at 1059 MHz core, 1125 MHz maximum GPU Boost, and 1752 MHz (7.00 GHz GDDR5-effective) memory, yielding a memory bandwidth of 224 GB/s. 

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.

The BIOS file can be found here (use at your own risk).

Flash a GeForce GTX 680 to GTX 770?