FYI I found out that RMClock does not support latest AMD CPUs. So I used K10stat. I was able to undervolt my CPU from 0.95 to 0.8V at full load (1300MHz) and from 0.85 to 0.7V at 800MHz...
Northbridge can also be undervolted but only form 0.83 to 0.8V in my case.
CPU temperature at full load is 62°C (tested with prime95 running on both cores)...
I will report back how this changes in CPU voltage influence on battery life. I got around 5 hours of surfing with WiFi on and screen at 7 out of 15.
Here is a good guide to start with K10stat:
http://aspiregemstone.blogspot.com/2009 ... essor.html