When you run them at 1.8Th/s how much power do they consume?
They don't stabilize very well even at 1.8 where I have them set-up (too warm, these were missing heatsinks on VRM or something around those lines). Power consumption is around 0.45-0.5W/GHs at current voltage/frequency. 2 of the cubes aren't even hashing right now.