Do you mean faster, more accurate, less hand movement? I'm just curious how we're measuring efficiency. I have carpal tunnel and used Dvorak for many years because I found (anecdotally, grant you) that it was less hand movement.
The origin of all positive claims regarding the dvorak layout came from one study by US Navy that has been discredited for at least 20 years. Because carpal tunnel (and similar ailments like tendonitis) are repetitive stress injuries, switching layouts would change the repetitions. http://reason.com/archives/1996/06/01/typing-errors/1
The Dvorak legend is not entirely without basis: It seems a more logical layout that really ought to minimize hand movement. Thing is: For trained and skilled typists, that seems to make no difference in ultimate performance. Matters may be different for people suffering, e.g., from carpal tunnel who are willing to invest into retraining their hands.