The GK104 is anticipated to feature 1,536 CUDA cores, but the large increase in shaders will not result in a linear increase in performance because NVIDIA has a adopted a different architecture. The source claims the GeForce GTX 680 is about 10 percent faster than the Radeon HD 7970 in Battlefield 3, but slower in 3DMark 11.
The launch date of the GeForce GTX 680 is set for March, but the cards will be available only in small quantities and only from select add-in board partners. Larger quantities are expected "in later months".
The mid-range GK107 chip is anticipated to be released in April, and a dual-GK104 should follow in May. The flagship of the Kepler family will be the GK110, this chip is rumored to have 2,304 CUDA cores but there's still no word regarding a launch date.
Sources: TechPowerUp and Heise.de