4ghz needs probably 1.5v, because it's not stable with 1.475v (with very good temps). I decided to leave it at 3.9Ghz for now and find the lowest stable voltages.
The lowest voltage for the CPU is 1.425v (down from 1.45v) - tested for 8h P95 blend mode. 1.4v crashes the 3rd core.
Regarding the RAM, I'm surprised to see that the system seems stable with 1.5v. My ram is 2x Kingston HyperX blu 4GB, DDR3, 1600MHz, CL9, 1.65V. I run it with exactly these settings (1600mhz, 9-9-9-24) and it is stable at 1.5v for 2 hours in P95 blend mode and 1 pass memtest86+. How come? I can't believe it.
Will I lose performance if I try to get the lowest possible voltages? My current "philosophy" is to get the highest frequency with the lowest voltage.
BTW: idle CPU temp: 21C in memtest. Which is again, amazing. My CPU fans just needed more air to push through that heatsink.