try bumping your NB to 1.55 and set your mem on the 5:6 divider and run 5-4-4-6 for your timings. Increase your Dram voltage to 2.06 or 2.08.
I too run 4 sticks of memory as you know the same mem as you. I have been playing with these settings trying to find a stable place for you to run your with a little more punch. I hope this is it for you.

In the bios I am running 5-4-4-6-6-30-6-4


WZ