920 is bloomfiled not sandy bridge, 45nm
Edit: my bad, misread.
The headline was very misleading.
A lot of DDR3 memory modules with XMP operate with 1.65v
If you can't post with 1.5 volts, bump it up, no need to use higher volts if your system is stable without it, forcing more volts trough transistor gates is more bad than good.
You'll utilize the 1.65 volts if you ONLY use XMP, and don't bump it up yourself. XMP is designed(and certified) to do what it does, so most probably you'll be fine.