av16 is supposed to draw 4A at conservative settings and upto 6.5A at maximum safe settings per http://drillbitsystem.com/forum/index.php?topic=309.0.
I estimate that a single board takes about 5-6A when doing 22 GH/sec.  At 5A it will be 5*12=60W, so 22/60=0.367 GH/W. (probably need to add a few Watts for the essential fans).
The Antminer S1 at default settings does 180 GH and takes 360W at the wall, which makes 0.5 GH/W.  This suggests that the S1 is slightly more efficient, however both are significantly less efficient than the S2 or Spondoolies SP10.

Cheers