The Masechet Sof'rim mentions that 175 Parshiyyos in the Torah is k'neged the 175 years Avraham Avinu lived
1. The so-called Triennial cycle actually was 2 cycles per Shemittah, or once approx. Every 3.5 years. This minhag apparently prevailed in E"Y during the. Era of Mascehet Sof'rim. I'm not certain precisely when that was. Probably after 500 CE and before 900 CE, but again I'm not certain
2. The notes in the Peirush "Bei'urei Sof'rim" cites the Yam Shel Sh'lomoh at the end of Bovo Kama who lists (all) the hilukkim between E"Y and Bavel. I haven't seen that, but I bet it makes for a fascinating read.
My chavrussa and I were M'sayyem Sof'rim with the Vilna edition along the Soncino English translation. The Vilna has an outstanding Peirush Nachalat Ya'kov plus hagahos from the GRA and Peirush "Kissei Rachamim"
The edition I'm now using for hazarah is based upon the Gra's Nusach and has a nice summary Bei'urei Sof'rim who suimmaizes the, N"Y plus other acharonim. I plan a siyyum for my brother's yahrzeit BE"H on 6 Iyyar.
Sof'rim is really a must read for "Minhag Addicts" like me.