The only true voltage indicator is a multimeter. The bios is just an indication - its still software in its most basic form.
I have found everest to be among the most reliable software based tools though along with the latest version of CPU-Z.
Most, if not all boards will have some form of Voltage drop (vdrop) from bios to windows and it will also drop (read Droop) again when the cpu is under load (vdroop). This is intel spec and not a design flaw. It is intended to extend the life of the cpus by lowering the potential risk of voltage spikes which can and do sometimes damage cpu's. Some high end boards have a setting such as voltage dampner or loadline calibration that will reduce the effects of vdrop but there is usually still some and the only true way to cut it down completely is to mod the motherboard either by a simple pencil mod, or by soldering on extra resistors to the mobo. Unless it is real bad then simply compensate the drop/droop by increasing the vcore.
Hope this helps.