I think all Gigabyte boards are good boards but, in the spectrum of boards, other boards will likely have a greater chance of succeeding at what you want to do.
Undervolting isn't unlike overclocking: higher voltage allows for cleaner switching at higher frequencies; lowering the voltage but keeping the same frequencies has the same effect: both are more sensitive to input power stability.
Now, how much will all this matter between boards? I doubt anyone who hasn't designed these boards can say without experimenting. I would say, a more robust board that may allow you to undervolt a little more would likely end up using more power than the basic board simply because it is more complex with more parts.
We are splitting really fine hairs here, so if power conservation is your concern, I wouldn't get wrapped around the axle about it. If you wanna just 'cos you wanna--I can understand that.