We stumbled upon some rather interesting details regarding the recently updated Nvidia 600M mobile lineup of chips and it appears that some of the Fermi chips will be switched to 28nm.

Nvidia decided to "build" its 600M series as a cohesive family of chips by targeting the right GPU for the right market segment. Since mainstream notebooks are more cost sensitive, Nvidia decided to go for Fermi based GPUs that will "offer significantly improved efficiency, paired with a cost effective design". Of course, this mostly means that 610M, GT 620M, GT 630M and GT 635M (and GT 640M LE that will be apparently based on both Fermi and Kepler) are actually re-brands and will all be based on Fermi architecture.

According to what we know so far, Nvidia didn't talk much about "improved efficiency, cost effective design and optimizations" of these Fermi chips, but we did notice that both GT 620M and the GT 630M are switched to 28nm process (GT 630M apparently as 28/40nm).

Unfortunately, the high-end offering that includes Fermi-based GTX 675M and GTX 670M will still stay at 40nm. Nvidia did note that despite still being based on Fermi architectures, the company is looking at "improved Fermi chips" that have been optimized to squeeze peak performance in an enthusiast notebook chassis.