There's a 108 page thread on the ZE over on the US OC forums, complete with tails of woe with memory. It's extremely hard to get above 3333MHz without going very loose or having 1.4V to memory and/or a SOC voltage above 1.1V (but no hard and fast rule on SOC voltage, just that it may need to be higher if you OC your CPU even if the memory was stable at stock). However you're 4 x 8GB so probably single rank - so you've got the best chance to hit your rated speeds. Those of us with 64GB - 128GB top out at 3200MHz on the 801 BIOS, haven't played with the new 804 BIOS yet, there is also an old modified 801 BIOS by the Stilt which is even better for memory. Asus has just about abandoned this platform, we got this new beta BIOS after 2 months of no communication from them at all. As suggested by lowdog run memtest (just buy the pro version for $5 so it automates testing the whole lot...) to find the random errors (over 600%) - you might feel stable but those random errors cause programs to crash. Like you I stopped at 3.95GHz (1.30V), above that required more V then I wanted, I actually run stock mostly (with 3200MHz memory) and then run the all core OC profile when rendering.