Interesting comparison.  Thanks for posting.  I have a 1971 SM9 (and a 1956 SM3).  I have read several comments that the SM9 was boring or unremarkable.  If I could only keep one of my 12 typewriters, it would be the SM9.  Great type quality, lack of drama, reliability, modern lines, quality build.

1955 Hermes Rocket
1954 Hermes Baby (restored)
1959 Smith-Corona Skyriter (awful)
1948 Smith-Corona Silent (typed out, but pretty)
1965 Adler Tippa 1 (British keyboard, purchased by Dr. Boyd O'Dell in Hamburg in 1965)  Daily driver.
1971 Olivetti Lettera 32 (daily driver)
1968 Webster XL-500 (Elite)
1967 Royal Mercury
1976 Olympia Traveller de Luxe (Brazilian keyboard)-came from a photo shop next to the Vatican in Rome, still has the shop sticker on it.
1971 Olympia SM9 (perfection)
1966 Olympia Splendid 33 ("Italien 4" keyboard, purchased 2020 new-in-box :-).  So nice to get to break in a "new" machine in 2020. 

I use the Mercury, XL-500, and the beat-up looking but mechanically perfect '55 Rocket in the field, alternately riding on the Yeti cooler behind the seat of my work truck.  Great field machines.  Started out using a '59 Royal Royalite in college to type all my papers (this was in the late 70s, early 80s-a miserable hand-me-down machine with a skipping escapement).