Set your memory multiplier to 2.00 like in the screenshot above. DDR is running at twice the fsb, so 2 / 2.0 = 1:1
2.50 memory multiplier is the same thing as 4 : 5 as 2 / 2.5 = 4 : 5
You get the idea. It seems each motherboard company has their own way of setting up the bios menu for the multiplier. Causes a little confusion.