Awesome that it worked. Each case is unique. My friend, living in the same city, with pretty much same immigration history, same country of origin, same occupation, same age submitted I-751 two weeks later than me - got approved 4-5 months earlier than me. Neither of us had interview, nor RFE. Same case pattern - different timeline.
The USCIS processing time changed from 7 to 12, then to over 14 months, then to 17. Took 20 in my case.
I could have tried VJ estimates, I doubt they would be anywhere accurate.