George,
Congrats on the QX. You may find this kind of crazy, but I think you are having stability issues because of your FSB. My findings have always led me to stability issues whenever FSB was near 445, 450.... I cannot even boot Windows after 450 FSB, 455+ it will freeze at post. So, FSB has been a huge limiting factor for air/water on these QX's. Just a little FYI from my personal experience.

Try 10 X 400 with 1.3625 (bios selected) vcore and if you have ample air cooling capacity I am pretty sure you should be quad prime stable set to (12meg cache setting in multiprime).

I know, because you are raising the multi, bus speed and ram will be slower. But I see you are running CAS7 6-6 on those sticks. To combat this I have found the best setting on a 4.0 Ghz overclock for me was:

10 X 400 , 1.3625 Vcore bios selected (1.31 after vdroop)
Ram at 1600 mhz, Timings: 6-5-5-18 (2.05v , 1T)

As you can see, even though you are lowering FSB, you still have the ability to run CAS6 and tighter timings + I am pretty sure you will be able to achieve 4.0 GHz low volts stability.

Let me know of any results.