I could have been lucky that time too, I haven't tried to accomplish that again. I am running 2.5-3-3-8 though at DDR540, so I know this memory is capable of a lot.
If I were you, I'd try to just up the voltage, maybe to 3.0 or 3.2 and then turn your divider to 1:1, to *try* for DDR520. I might tri 2.5-3-3-8 as well.. and if it's not stable, I would blame your CPU. The new Venice chips overclock very well apparently.