by default timing, do you mean 11-11-11-28? sometime CR shows up as 1T other times 2T, and there's not an option on my mobo to manually control it. I have a biostar tpower x79.
i've tried 13-13-13-30 @1.5v, and i still can't push the memory multiplier any higher.
with 9-10-10-24. i need to give it 1.5v to run 1666.6 mhz.
edit: 4x4gb ram. i'm not sure if this makes a difference. vccio = 1.092v