Are you using the latest BIOS? Also, make sure you select Expert and not Quick (or whatever it is called) for the memory settings.
Strange thing though. Now I cannot do any overclocks what so ever, the PC just gives a black screen each time I try anything and doesnt post at all... I have to clear the CMOS to get back into it. When I say I cannot overclock, I tried OC from the default 143 CBLK to 144 CBLK, which is like a 19MHz increase. I tried entering the memory timing and the same. I reset it each time and tried again. I even re-installed the bios, in case something went wrong. It just doesn't work.
So, i am back to F5 now and it overclocks again. Very strange indeed.