Post #8 in this thread includes hardness tests of various Parabellums. While the author cautions that the sample size was small, the data tends to support the oft-read assertion that steels used in Parabellum manufacturer got better (harder) over time.
http://luger.gunboards.com/showthrea...irst-Stock-Lug!
Broken part survey in the FAQ is interesting although not definitive.
http://luger.gunboards.com/showthrea...-the-Luger-FAQ
This article strikes me as informed opinion, and is critical of the pistol.
http://www.forgottenweapons.com/wp-c...unFacts%29.pdf
I have wondered the same as the OP, and like the OP prefer actual data. Here in Colorado we have world class experts in metallurgy at the Co. School of Mines; this thread reminds me that some day I'd like to take a few Luger components out there and see if they would test and comment re: metal quality and suggestions for preservation.