I think you are looking at the DDR voltage control. I'm undervolting a BE-2350 in that MB @2.1GHz at 0.975V in the BIOS. Speedfan shows the voltage varying from 1.01 to 1.02 under load.
The BIOS allows control of the CPU, DDR, and NB voltages separately. The CPU voltage range is silly. It goes from just under 2V to way under 1V. The DDR voltage starts at 1.8, I don't know that there is any reason to go lower. I haven't looked at the NB voltage control, yet, so I don't know what it can do.
My temp3 is 77-78 at idle. I have driven it as high as 106 before instability. I think that temp3 is really the GPU internal temperature, since I could move it directly by overclocking the GPU, independent of load. You might want to check that your NB heat sink is correctly mounted. Mine rocks back and forth if I push on either end.
I'm going to replace my NB heat sink with a Thermalright HR-05 IFX since I'd like to try to lower the temp on it and would like to have reliable contact between the heat sink and the NB. I'm waiting on delivery of some 80mm Thermaltake Smart Fans. One will be on the HR-05, the other on the CPU HS. The CPU Smart Fan Control is set to turn the HS fan off if the CPU is below 40C, so it doesn't run most of the time. I'm going to run the NB HS fan off the same header for the same reason.
I have the board in an Antec NSK-2840 chassis with the stock 380W power supply. I replaced the two 120MM Antec tri-cool fans with Thermaltake smart fans. I'm using the thermal controls on the 120mm fans so they both spin under 700RPM at idle. They only speed up if the google image screensaver is running.
I'm not using the stock CPU HSF. I put a Ninja Mini on and am running it essentially passively. Running two instances of Prime-95 with both cores at 100% barely gets the CPU up to 40C at 26C ambient. The NB runs ~82C. At idle the CPU runs 2-5C above ambient.
Kill-O-Watt shows my system consumes 47W at idle and 59W during the stress tests. The undervolting takes 4W off the idle wattage and 12W off the stress test.
Antec NSK-2480 with two Thermaltake 120mm Smart Fans
BE-2350 with 10x multiplier, .975V in BIOS, clock at 210
Ninja Mini CPU HS
GeIL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800
Seagate 500GB SATA hard drive
ASUS 18X DVDÂ±R DVD Burner PATA Model DRW-1814BL
I'm running Windows XP Pro.
If you play around with the CPU fan control in EasyTune5-Pro, don't set the low percent below 10. 10 is low enough to turn the fan off at or below the low set point. Less than 2% will lock up the system. You can set the high within a degree of the low. Setting it the same or lower will lock up the system. The only way to get the system back in either case is to un-install ET5. It takes forever to install, so save yourself some time and don't try to prove me wrong