That turbo voltage setting is something that people often won't know. I didn't see it on Gigabyte, only saw it with ASRock. That means you have to be careful when talking to people. There could be miscommunication about offset and turbo voltage.
Generally, people are interested in that offset stuff because it's needed if you want the voltage to go down when the CPU is idle. Voltage normally drops to something like 0.8 or 0.9 V at idle. If you use fixed voltage, it won't go down.
The offset voltage is something that gets added to the stock voltage. Your CPU has its own unique "VID" voltage it demands. It's set by Intel in the factory after testing each CPU by itself or something. If you don't use fixed voltage, "Vcore" is the result of "VID + Offset". Offset will increase (or decrease) everything, including the idle voltage. Idle voltage will still go down, but it will be higher than at stock.
Offset is a flat value. That means if you used fixed voltage until now, you can deduce your offset voltage if you know your CPU's VID. I know my CPU has VID 1.18, and I know it is stable with my overclock at 1.255 V. This means instead of fixed 1.255, I can use offset +0.075.
ASRock has that turbo voltage stuff. The dude that wrote the ASRock overclocking guide for Ivy Bridge suggests you keep the normal multiplier at stock (35 ?), then set the four turbo multipliers to 45 or whatever you want to overclock to. You then go and increase the turbo voltage, don't touch the offset voltage. You leave offset voltage at the lowest positive value that is available.
I have no idea how the turbo voltage setting actually works, if it's the same formula as for offset voltage but only for when turbo is on, or if it's something more complicated. I can't say anything about how to translate it to fixed voltage. It definitely sounds like a better setting to use than offset, as it won't increase the voltage if the CPU gets downclocked at idle.