Since March, the fastest members of the GeForce GTX 600M series have been older, 40-nm GPUs based on Nvidia's Fermi architecture. No longer. Nvidia has announced the GeForce GTX 680M, a new mobile flagship featuring the same GK104 silicon as the desktop-bound GeForce GTX 670, 680, and 690.
The 680M shares its desktop namesake's 32 ROP pixels/clock, 2GB GDDR5 memory capacity, and 256-bit memory interface, but it has fewer shader ALUs (1344 instead of 1536), can filter fewer textures per clock (112 instead of 128), and clocks its core and memory lower: 720 and 900MHz, respectively, down from 1006/1500MHz.
The GTX 680M will be available in some real notebooks soon. According to Nvidia, Alienware plans to add the GPU to its jumbo M17x and M18x gaming notebooks "in the next couple of weeks." With the M18x, you'll have the option of getting dual GTX 680Ms in an SLI setup, though that particular config might not be available until the end of the month. MSI, Ava Direct, Maingear, and Origin all plan to offer the GTX 680M in their laptops, as well.