That's efficient if you define efficiency as hashes computed per watt. That's the metric by which less-efficient miners are driven out. However, this does noth

That's efficient if you define efficiency as hashes computed per watt. That's the metric by which less-efficient miners are driven out. However, this does nothing for the overall energy efficiency of Bitcoin, which could be defined as transactions processed per gigawatt. If energy gets cheaper, that number only gets smaller.