Nvidia tests M2 chipsets
 

It is said there that there will initially be three versions, the low end MCP55 Ultra, a curious name for a low end chip. It will have 20 PCIe, six S-ATA ports, 2x Gigabit Lan and UAA audio if that report is to be believed.

For SLI, there is the MCP55P SLI and the MCP55PXE + C51XE positioned as the top dog. The SLI has two 8x slots and 12 more lanes apparently, but the rest is the same as the Ultra. I would guess this is actually the same chip as the Ultra, just fused differently.

The top end XE + C51XE has two 16x slots and 14 more, while adding RAID-5 to the drive capabilities. It is also said to be 'very overclockable'.