I have 800MHz and managed to get from 2.66GHz stock to 3.8GHz by dropping to 775 MHz, you don't have to go a full load down, just a few MHz can often do the job.
voyager, do you have an option to change the memory frequency, if so, that is the one that you want, drop it a little.
Also, before you do, open up CPU-z and look at what voltage your memory is at and knock it up a little, very often when overclocking your CPU gets more power, but your memory gets the same as before, even though it is having to do more work because it is throwing information at the cpu and taking information from it more than it was before the OC
=EDIT=
should say, if you do raise the temps, be careful, do it and after a few minutes and a stress test, pop the side off of your system and put your fingers on/near the memory and feel if it is hot, often when you raise the memory voltage it can cause a fairly significant raise in the heat, which can be bad news if you don't have decent head spreaders and air flow on your memory and in your system
