Putting these mobile chips into unknown motherboards can be a tricky thing. There's no real good guide as to how a new motherboard type will react.
Mostly likely it will limit you to the same BIOS options for voltage that you see now, with 1.55 being as low as you can go. While not as nice as being able to drop to 1.1v like you can on some other motherboards, it's still better than running a desktop chip, since you have full control over the FSB and Multiplier too.
Going from the mobile default of 1.45 to 1.55 will only bump your wattage by 6 watts, which is really pretty small.
There are a couple of other options for you too:
. 8rdavcore has some support for your mobo. That might let you drop the vcore lower than you can in the BIOS. (but you won't know until you try, unfortunately)
Get a new mobo
There are lots of motherboards that are known to undervolt well with the mobile chips. You could sell/trade one of your K7N2G for one of them. (have a look at the NF7-S if you go that route)