The reason for your speed to drop is that you have speedstep enabled.
try starting with a bclk of 160 (this will be no problem at stock vcore) and set your ram to its stock 1600.
You will need to bump up the ram voltage to its rated 1.65v.
You may need to set the timings manually. 7-7-7-24 are the stock settings. Best to start here.