Quote Originally Posted by Sam_oslo View Post
800MHZ was the norm at the start av i7 C0, but i7 has evolved and most D0's will do @4.2-4.4GHZ 24/7, and this is the BCLK210 territory. 840MHZ has become the "not so nice an round" number that creates a big RAM-dilemma (many sticks can't run at this speed even with higher voltages). I guess many of these "strange" stability problems starts when people try to push the RAM over it's limits.
imho is not only RAM issues, I think these problems are related to CPU Integrated Memory Controller and QPI bus frequency.

Not all the CPU are abe to run with uncore > 3.6 GHz and/or QPI bus strongly overclocked: BCLK>190 MHz and then QPI bus >190x18=3420 MHz.