VR-Zone have a very tasty nugget of information regarding NVIDIA's 28-nm based Kepler GPUs, the first of which is the GeForce GTX 680. We're looking at the GTX 680 sporting 1536 SP, and 256-bit memory. It was rumored to not feature shader hotclocks, but it does.
The core should be clocked in at 705 MHz, with shaders sitting at 1411 MHz, this continues to 2x shader hotclock from Fermi. GK104 also significantly improves upon the GF110/GF114's memory controller, where it pushes boundaries right up against the fence to 6 GHz. What this will provide is a memory bandwidth of 192GB/sec, identical to the GTX 580, even though it has a narrower memory bus.
The GeForce GTX 680 will sport 4 display outputs: stacked dual DVI, HDMI and DisplayPort. One disappointing feature is it only features two SLI connectors, enabling only 3-way SLI. Considering the GTX 580 could handle 4-way SLI, this is quite strange. The GTX 680 is said to be 10-inches long, 0.5-inches shorter than its predecessor. This makes it longer than the GTX 560 Ti or HD 7870, but shorter than the HD 7950 and GTX 570.
NVIDIA will reveal details of the GTX 680 on my birthday of all days, March 12th. We should then expect a hard launch (rumored) for March 23rd.