Max 350 MB/s on SEQ. Need assistance

IIRC that board has 2 different SATA controllers for the 6Gb ports. I cant remember exactly but i think it either has 2 intel ports and 3 Marvel Ports or 3 marvel and 2 ASMedia ports. Either way one of the SATA 6Gb chipsets is very slow for SATA 6Gb. Try plugging in into the other set of SATA 6Gb ports.