AM2 seem to grove on the voltage much like the 939 Optys when on air. In your case with phase, you have plenty room to up the voltage as necessary. Personally I recommend, which you seem to have doen, is get the most out of the default, then up it a notch and work up the OC some more, continuing with that addage untill you find it's max.
Consider the method in the link below to find each components abilities!
BTW, many manufactures use the Ballistix "Micron" ICs and are known to OC well so I doubt they are an issue. There voltage settings and timings may need some adjusting.http://www.overclock.net/faqs/31782-...pu-memory.html