Malzig: Thanks for the link to Kai's experiment. My efficiency is consistently 70%, +/- 1-2%. I might try a longer mash next time and see if that boosts my efficiency.
I remember hearing an interview with Dr. Bamforth where he talked about dextrins and beer. In a blind tasting, they doctored a light lager with pure dextrin. It took a huge amount of dextrin, like more than you'd ever see in wort, to get even a slight change in the apparent body or texture of the beer.
Proteinases should be active up to 155*F in the mash, so I wonder if, with highly modified malts, the effects of high temp increasing body are the result of less protein degradation, and don't involve dextrins at all.