Arsemonkeys - just finished unlocking my chip (sempron 2400+), tinkered around with CrystalCPUID, looked like I got a stable setting of 5x multiplier (840mhz off the top of my head) and 0.925V, then checked MBM - VCore = 1.65V (default). Checked BIOS and it only overvolts (Auto, +5%, +10% and +15%).
Looks like there's little point using CrystalCPUID then as the chip's already pretty cool on idle (thanks to using the S2K disconnect).
Any other options? Would flashing the BIOS help? OCinside's interactive pinmod thing shows you can lower VCore using some pinmods, but you need to cut all the L11 bridges which sounds a bit drastic.