I quickly tested my V5.11 kit on Phenom X6 and got up to DDR 1800 CL898 24 1T @1.55V.
Going higher with volts would probably gain few more hertz but I didn't try as this was sweet spot for my CPU/NB/HTT clock.
1740MHz at the same timings was stable with 1.5V

For that price I wont complain, but OC is not something this memory was made for.