that really depends on which cpu you have in your possesion.
my old 4200, it has a x 11 multi. if i drop it to 10, it will overclock my ram so much my rig wont even boot up.
on the 590sli, i notice that it does not like to have the cpu multi lowered, especially when overclocked.
you really have to monkey around with the cpu multi and ram speeds to find the best combinati0n.