Source: https://forums.butterflylabs.com/blogs/bfl_josh/386-monarch-update-30-april-2014.html
Butterfly Labs released new test data for the 28nm chips slated for their upcoming Monarch and Imperial Monarch miners. The results are highly encouraging, hitting a benchmark of .27W/GH at 400 GH/s, At higher voltages, the Monarch is testing at .55W/GH at 1 TH/s. According to the BL forum post, this next-generation machine will result in a massive boost in real-world mining power.
What does that translate to in real world numbers? At our nominal speed for the Monarch, 600 GH/s, power consumption is about .3W/GH at the chip level. We expect it to draw around 235W at the wall. The Monarch can be overclocked to approximately 800 GH/s per chip, or 1.6 TH total per board with specialized cooling.
The Imperial Monarch is expected to consume about 550W at the wall at 1 TH/s. The Monarch product line is essentially 3x - 5x more efficient at any comparable hashrate than the competition, which should allow you to run your Monarch for much, much longer than any other bitcoin mining device that exists now or that is even planned for the next generation.
With a new range of 28nm chips hitting the scrypt ASIC market in coming months, the BL Monach line offers some encouragement of similar leaps for hash-hungry bitcoin miners.