From what I can tell, the M880G chipset with the 4250 graphics card is paired with the SB820 southbridge, which does have SATA 3 (6gbit). If the laptop has the SB810, it does not have SATA 3. There should be a lot of programs to tell you what hardware you are running.
If it is connected at SATA 3 speeds, the device is being limited by a device up the chain.