Won't scale to 72GH/s for 340 USD... more like 10.000 USD, which is in line with what Avalon is charging.
BFL might be trying to get economies of scale as they (possibly) realized they shot themselves in the foot with pricing. Then again, their ASIC is on a smaller process so each unit might be cheaper than the Avalon ones (so many variables...).
The Avalon 66GH/s has been measured at 620watts by at least one owner, and uses 240 chips that run at 275MH/s not 300MH/s even at 300MH/s we would be talking over 40watts per 16chip Klondike board. Personally I would wait until the chips have arrived, been fitted to a board and measured running before making efficiency and cost claims. You might suddenly find the 16 chip board needs more cooling or who know what other issues.