Hmm, that's not very good.
I'd assume the CPU's OC is holding you back.
Switch to a higher ratio, such as 4:5 or 2:3, to to test for the RAM's max.
Obviously, that will be a lower CPU speed, but in order to find the max RAM can do, you generally have to lower the CPU's speed.
If these are Powerchips, they should do over DDR2-1000 5-5-5 @ 1.9-2.1V.