3> 645MGs are great for 40-60 size aerobats and 1/4 scale "scale" flyers, but no good for IMAC or 3D planes like the Edge, you are asking for trouble if you use these.
Sorry, but the HS 625MG's on 6 volts does just fine on my 30% Edge. If you just want to spend money for the sake of spending money, then go digital. The 625's hold up well and are plenty strong for the average person. IMHO