hi, i am building a new pc and am buying an Asus P6T board and a W.D Sata 6Gb/s hdd. Are Sata 6Gb/s hdd's backward compatible as the Asus board dont have support for it. If its backward compatible then will it be making any difference in its speed and wat if i buy an Asus U3S6 add-on card for it, will it have any affect on the speed.