Mr Berto has performed a great service, and this I don't deny. I read his original performance article back in 1980 or 81 and I was fascinated. Here are my views on the same subject.:
First rear derailleur performance is only really important when we are discussing horrible to adequate.
Horrible : Campy Valentino, Simplex low-end cheapo plastic...(These for me simply worked only well enough to cause frustration and doubts as to my ability as a mechanic and or cyclist.
Adequate : Suntour Blue line, Suntour Cyclone, Suntour ARX (good but not durable - only lasted one year), Suntour Superbe Tech (only slightly more durable) , Suntour Superbe Pro, Shimano Altus, Huret Alvit (my old dependable for five hard riding years)
Delightful : Suntour XCM mountain indexed, Campagnolo modern 10 speed Ergo,
Ethereal: Shimano DT 7 speed indexed 600 series., Sturmey Archer 3 speed. (bullet proof to boot)
Finicky : Shimano STI (and ugly to boot)
Soon to be tested and in hopeful anticipation: Campy Super Record early 80's vintage.
Alas, I don't believe I ever put in any serious mileage on any thing else other than these. I can live with anything in the adequate category and above, but I would avoid finicky or horrible. Other than that it's not about the shifting mechanism, it's all about the shifting cyclist.
Garth Libre in Miami Fl.