Thanks for reviewing the bios.
I did 10-15 passes on each module with memtest and no errors found.
I am doing the following test: I've put the greens back into the system and I am running only 2 ram modules instead of 4. XMP enabled... and, well, so far no bsod...
It does seems that there is an issue with timing and voltage, as suggested, with all four rams.
At least I know that I have a stable system if I want, but I would prefer to run the 16g set (noticed improved speed over the current 8g setup) at 1600... any idea how?