The MCP78 is for the AMD AM2+ Phenom processors while the C72 and C73 are for Intel's 45nm Yorkfield and Wolfdale CPUs. The biggest difference between C72 and C73 is the difference in memory and FSB support: C73 supports 1600FSB and DDR3-1600 and C72 supports 1333FSB and DDR2-1066/800.
There are 2 variants to each series of SLI chipset; XE and P where XE supports 3 x16 SLI priced at US$150+ and P supports 2 x8 SLI priced at US$100-120. Only MCP72 series can support Hybrid SLI. C72 early samples will be available to customers by end of July where mass production slated for October. MCP72 early samples will be available by August with MP targeted for November. C73 will arrive later where early samples targeted for November and mass production in December. So we can expect MCP72 and C72 to be on target for launch together with G92 in November.Source: VR Zone