set CPU multiplier to 20x
set voltage to 1.4 V
you will end up with 4GHz.
have you tried unlocking the 2 extra cores to make it a 6 core CPU?
and there is no particular configuration, it is completely dependent on the CPU itself. one CPU may do a gazillion GHz and another may do only 3 ;p
you need to download prime 95 and test the stability later, by running it for atleast 8 hrs (overnight)