I know the speeds aren't supposed to be exactly what they are advertised, but mine are at about half what they should be. I am running in AHCI mode and I did a fresh install of windows when I got it. The drive is about half full.
For note: Sata 3gb/s means SATA II ports. Sata 6gb/s means SATA III ports.
Therefore, your motherboard only has SATA II ports.
However, don't let that disappoint you as the benchmark doesn't mean much, given that your actual real-life usage of the SSD will differ from what the benchmark tests.
Do a WEI test on your SSD and see the score for yourself; it should be above 7.0.