The VID is the "stock" vCore for each chip, and it varies from chip to chip of course. The VID tells the motherboard: "This is the voltage I require at stock speeds when the VCore setting is on 'Auto' for proper operation." That's it.
Your "Cpu Voltage" is what your cpu is currently being fed.
This is what I have found with a little experimentation though: both CPU VID and CPU Voltage seem to have an effect on the vCore. The problem though is that I'm not sure how much of an effect each actually has respectively.
Setting the "CPU Voltage" to 1.6 results in a vCore of 1.4 in the BIOS, but Core Temp--the only monitoring program that I've found which doesn't give me a reading of .976--will continue to show 1.325 if I've left the CPU VID @ stock..
On the other hand, changing CPU VID impacts both vCore in the BIOS and in Core Temp readings. What's strange is that I get two different readings in BIOS and Core Temp, with core temp's always being lower, but never a constant value lower. For instance, stock CPU VID will give a vCore of 1.36 in BIOS and 1.325 in CoreTemp (difference=0.035) and another CPU VID value will give a BIOS reading of 1.39 and CoreTemp of 1.3625 (difference=.0275)...
Also odd, is that CPU VID's values seem to have an inverse effect on vCore. CPU VID is in hexademical, so when I input lower hex values, I end up with higher vCores. With vCore, I can at least check the resulting values from changing CPU VID in my BIOS/Core Temp so I can see whether there's been a positive or negative effect.
This leads to a bit of uncertainty in another area. See, my NB VID, NB FID and CPU FID are all also in hexadecimal, but for these settings I can't see the resulting values from my manipulations--at least, i don't know where to look for them. Therefore, I have no idea whether these other options are likewise inverse like CPU VID appears to be, or if they aren't...
Oh and by the way, my mobo, which i've added, is a EVGA nForce 730a, which i'm getting increasingly more frustrated with... well, that and my bios.