I'd much rather work from my own experiences. In my experience, the same stout brewed with a mash PH of 5.3 had a harsh, bitter roasted malt flavor. It was a bit acrid, thin in mouthfeel and unpleasant to drink. The same beer, re-brewed with a mash PH target of 5.5 possessed a more rounded, smoother roast profile. It was a much more pleasant drinking experience.
I quoted Martin Brungard's work because it falls in line with what my experiences have shown me.
Some of the things highlighted in Kunze's work above have not proved out in any real-world brewing (both home scale and production) that I have ever witnessed. Extract yield in functionally the same as long as the PH is within the acceptable range. There was no perceptible difference in lautering. The flavor being mellower, fuller and softer? Not in my experience. Lower mash pH tends to be sharper, with a thinner mouthfeel. I've never had a measurable difference in attenuation, either. Case in point? The stout above. Original and Final gravity was the same in both beers despite the mash PH being different by .2.
The only issue I have with your post is you are promoting information that has been proven incorrect. Doesn't upset me in the slightest but I felt that anyone stumbling into this post that doesn't know better might be led astray by blanket statements.