I've used a version of Kai's documented Hochkurz method for a few brews. I'd say that the Fermentability and Mash Efficiency are improved. I haven't done side-by-side tests but know in comparison to other single infusion brews the numbers are better. Accident? Maybe, but I tend to think the modified double decoction makes a difference. If for nothing else to justify my time & effort.
. For example. A recent Weissbier produced 90.4% BHE and the WPL380 took it from 1.052 to 1.008, ~85% Apparent Attenuation. I generally run in the ~82% BHE range for ~1.050 beers and the AA varies with the yeast.
Just last weekend I did a Doppelbock/Bock Partigyle utilizing a modified double decoction. Both are fermenting right now with slurries of 34/70. I don't have the AA yet obviously but the BHE for the batch was ~85% which is way over what I expected for 33 lbs. of grains & 10 gallons of beer where the Doppelbock OG was 1.100 & the Bock OG was 1.076 after blending the worts.
It's not scientific by any means but in comparison with similar brews, the modified double decoctions have been more efficient, and tasty I might add. The results have had their rewards. A Weissbier was Honorable Mention at the 2010 NHC Finals and a Strong Scotch Ale won BOS at the Nebraska State Fair and BOS runner up at our County Fair. Coincidence? Maybe, but I plan to continue to invest the time & effort into the brews that lend themselves to decoction mashes. Cheers!!!