I downloaded the manual for your mb so i could figure out how to change the memory frequency for you. If you change the dram frequency from auto to ddr2-1066 then it should keep the memory close to its rated speed. I run my ram at just under 2.1v and its rock stable at 960mhz. That should help you get your oc up some.
Edit: going to open a new thread like ACHILEE5 suggested.