Won't run at rated speed...

[Threshold]

My overclock is unstable when I have my CPU at 3.2ghz (orthos tested CPU only 12hrs and passed) and the ram running at the manufacturer rated speed (1066mhz 2.3v). It is however, stable when the ram is running at stock.
I have run mem tests and all seems ok.
Should I expect not to be able too run at optimised speeds with a clocked cpu? As it runs fine optimised with CPU at stock

 

[Bomag]

I found the same with my Asus 680i board. Having played around a bit I found that 4-4-4-10 1T at 800mhz with an o/c FSB was slightly faster than 5-5-5-15 2T at 1066mhz, stock FSB.

My P5W HD had a similar issue but only above 375mhz FSB.