no buddy ram dividers are different things. As u know that when we increase FSB the ram frequency also increases automatically.
Now if FSB:RAM ratio is 1:1 (which is ram divider) then if we increase FSB by 1MHz then ram frequency will also increase by 1MHz lets say from 667Mhz to 668.
Similarly there are many other different ratios like 1:2, 1:4 etc Now in ur mobo u don't hav them and u also don't have 550Mhz option which is must if u wana overclock 667 rams so u can't overclock more coz ur rams might already be running around 750Mhz and to go pass 800Mhz or more is pretty difficult. So i'm afraid u can't overclock more