On my board (M3A79-T Deluxe) Everest reports the SATA controller (and IDE) are on 66Mhz PCI controllers. At a guess that would limit them to under 250MB/sec. Everest does state the soutbridge is an SB700, when I know it should be an SB750 though, so I'm not prepared to say I'm 100% convinced by the results.

As for a BIOS update 'fixing' issues like this I'm less than convinced that's possible. Is this problem not more likely to be due to the way the PCB is traced rather than the way the BIOS works? I'm asking because I don't know...