We've seen AMD's plans for new Southbridge and they managed to get a lot of features that were missing in the previous ones.

SB600 had 4SATA ports, SB700 got that number to 6 SATA 2 ports while SB800 will get a brand new SATA 6Gb/s, probably branded as SATA 3.0 standard. SB750 added RAID 0, 1, 5 and 10 and 12+2 USB ports and SB800 inherits these features.    

In addition to that Gb MAC and the new clock generator, the SB800 features PCIe Gen 2 x4 support. This Southbridge will work with RS880, RS880C and RD890 chipsets, whenever they come out.