Just tried DDR3-1866 8-8-8-24 at 1.7V/1.75V/1.8V/1.85V
1.7V & 1.75V = no POST at all
1.8V = Pi 32M 'till loop 1 or 2
1.85V = Pi 32M 'till loop 6 or 7

1.9V yesterday gave...nothing, not even initial value calculation.

Not going to give up on them easy ( never did, even with the worse HW I've ever touched )...but I don't feel like they'll ever work full stable at DDR3-1866 8-8-8-24