It's 1W/Gh/s @ 100Gh/s at the wall, the efficiency is the same no matter how you clock and volt it. They even mentioned this fact when they first got their chips.
pls link
Efficiency for now is fixed cause voltages are locked @ 0,8 V, so by real measurement X1 has the same W/Gh/s clocked at 800Mhz or 1000Mhz. Let it run @ 500Mhz and drop the voltage @ 0,6 V et voilà efficiency will magically rise. Losses on voltage regulators will drop too. Every chip has its own limits but can perform differently depending on the working zone.
If the control board is capable of this ( there are some post where i ask it) what are they waiting for
