A rumor from Chinese forums Chiphell suggests that Nvidia has pushed up the release of the GeForce GTX 680 to February, over previous planned March/April time frame. The source says the GTX 680 should be competitive in performance with the HD 7970. The GTX 680 will have a clock speed of 780 MHz, which is similar to the GTX 580. It will come with 2 GB of memory. It is suggested that the card with have a 512-bit memory bus but this has neither been confirmed nor are there much details of the final specifications for the GTX 680.
Based on the leaked information, the card doesn't look like it will be Nvidia's fastest next-generation GeForce Kepler chip. It sounds more like the GK107 chip with a 128-bit memory bus previously discussed in December. Hopefully Nvidia isn't rushing its next generation GPU to the market, as this writer remembers the GTX 280 release. That card didn't shake some of its noise and heat concerns until the GTX 285.