Even after my research into guitar string composition and my re-discovery of Monel strings, I still find that Martin SP 80/20 bronze strings are the best sounding strings for my acoustic archtop, an Eastman 805. After trying several brands, I've found that Martin SP 80/20s have an excellent lifespan, and the best sound for the guitar. And now they are on sale at www.stringsandbeyond.com for 2-for-1 on their already excellent price. Since they are only $4.98 to begin with, that brings them down to $2.49/set - it's a ridiculous price, and I just stocked up.
While I still don't have the full picture of the introduction of bronze strings, I've drawn the inference that they were introduced in the 1930's to create a fuller and louder sound for "orchestra" archtop guitars and the newly introduced dreadnaught and jumbo flat tops. The D'Addario website mentions that "80/20 Bronze, commonly referred to as brass, is the original acoustic string alloy selected by John D'Addario Sr. and John D'Angelico in the 1930s." This leads me to believe that 80/20 was at least relatively close in time to the swing era, and given that phosphor bronze is 92/8, and was developed later to make a brighter, longer lasting string, I would posit that earlier bronzes may have been going the other direction. 80/20 bronze is the warmest bronze alloy currently being used, so I'd say it's the closest thing to the bronze used in the 30's, if not the same.
Having experiemented with the Martin SP "Lifespan" coated strings, I have found that they do not sound as good intitially, and even if they did, they do not last enough longer to warrant their increased price. Further given the ridiculous sale on at www.stringsandbeyond.com, they are cheap enough to replace regularly. So, it's Martin SP 80/20's for me.