Ouch - I have a Sata II drive that has better sequential read & write performance than that.You may want to try a different benchmark tool.. HD Tune is one example.May want to check the firmware on the drive & on the motherboard to ensure everything is up to date.Google to see if there are any known issues with your drive, your motherboard, and the combination of the two (im not doing that for you).Looks like all the ports on that board are Sata 3 based on Newegg's info. I didn't research any further than that. You may want to to be certain.
I have done all of that yesterday. And yes it is set to AHCI mode in the BIOS.