fwiw, I have everything in BIOS at "default" and use K10Stat for all settings. At my P3 state in K10Stat, I have:
CPU Volt: .75
NB Volt: 1.0125
I could probably go lower with the NB, but I've been running this config for years and it's just rock solid.
I've used PMSRT also, works the same, I just like interface for K10Stat better. You can also try TurionPowerControl (on AMDZone.com), it's amazingly flexible, but all command line.
Thanks. I'll leave everything at default in BIOS then and just use PMSRT to adjust.
At the moment I'm using 0.95v (down from 1.1v) for the CPU at P3 (800Mhz) but I'm sure it can go lower. For P0 (2800Mhz) I've tested
Idle: CPU 37, Core 26, MB 41
at VID 1.40 (default)
IntelBurnTest (Standard, 5 runs): CPU 55, Core 45, MB 43
at VID 1.35
IBT (Standard): CPU 52, Core 44, MB 44
at VID 1.30
IBT (Standard): CPU 51, Core 41, MB 43
at VID 1.25
IBT (Standard): CPU 49, Core 40, MB 42
So there's a nice reduction in temps (and of course energy) with each decrease.
P2 (1600Mhz) and P1 (2400Mhz) are still at 1.1v and 1.2v (1.2v and 1.3v default) so I need to work out what I can get those down to as well.
I'm not so sure about undervolting the CPU-NB as I'm running 1333Mhz DDR3 and I don't really know what depends on the CPU-NB.
EDIT: At 1.25v it BSOD within seconds of starting OCCT Linpack test, even though it passed IBT (Standard), so I increased it to 1.30v and it seems stable with that.