Get Gigabyte D3A mining board or even better Asrock h81 r2.0 mining board, i belive its more plug&play. You might have some problems getting the 6th card in Gigabyte board.
buy 6x amd 570 4gb. You will need atleast 1000w psu. maybe get 2x 700w.
how much mh is the total of these 570 amd 4gb? Also how many psu i need 2 only? Tell me how much power they will use (for electricity).
Also what i need for 300mh?