Used TechDAS Air Force III vs New Feickert Firebird with Kuzma Safir 9 vs SME 20 MK 2

I have a Stabi R with the Safir and continue to find more and more to like about the combo and how it brings out the best in a wide range of recordings. And this takes place without imposing any kind of "sound" on the source, instead leaving the impression of hearing what took place during the recording.

That said, I would want to know more about the kind of music to be played. I primarily listen to acoustic jazz from the 50s and 60s (think Bill Evans, Art Pepper, Oscar Peterson) so there is that. I also have moved to all tubes and recently switched to Joseph Audio Perspectives, so I would give some thought to how the combo will integrate with your other gear.

I don't know the other combos you are considering, so I hope this obviously biased perspective is at least slightly helpful... 

I also play rock at times, ranging from Steely Dan to Foo Fighters to Pearl Jam to softer stuff like CSNY or Van Morrison. All of it sounds more present with the Safir (and my current cartridge which is a Koetsu Rosewood Platinum.)

For what it's worth, I know of someone else who planned to add a second tonearm, but after a month with the Safir, simply didn't see the need. 

@clearthinker I am not any kind of engineer nor do I have enough physics knowledge to try to answer your question. However, I do know what I hear (and am fairly confident in not falling victim to owner's bias) and I consistently hear what I described earlier.

For a truly technical point of view, Fremer's review is quite complete: https://www.theabsolutesound.com/articles/kuzma-safir-9-tonearm/