QUOTE(Cyrus2k @ Sep 1 2006, 11:35 AM)
Well, now had installed the dual core optimizer. I had also flashed into the newset BIOS (using the windows flashing utility)
Thanks for the advice on voltage increment, now I found that my proc could run at 255x10 = 2.55GHz @ 1.425 Vcore
But there is one starnge thing I found; when I put the 1.425 Vcore in Bios, it will show as 1.440 Vcore in cpuz. Does this mean my mobo giving some extra Vcore to the proc?
At 2.55GHz, I could pass super pi 8M & 32M but unable to get pass Stress Prime after 5 minutes...
At 2.6GHz @ 1.45 Vcore, could not pass 8M (restart automatically)..
I dunno whats limiting my comp now...

You can pass 32M, but failed prime...
My tips is check the ram first. Use BIOS built-in memtest and let it run for a while and see whether got error or not. If there is error, you need to tweak the RAM a bit more, loosen the 'special timings' or add voltage 1 notch if needed.
If there is no error, try add slightly more cpu voltage like 1 notch for example. And try prime whether can pass already or not. If you can pass the test for like 1-2hour but will get error after that, back off 1MHz off the FSB and try run CPU Burn-in (no error detection) for 8hours, then try add 1MHz again.