One of my first Civ 2 games (deity, std barbs, large, random map, 7 players) I went overboard and decided to max the score, which topped out at 15,500 I think, in 2019 as my spaceship landed. Don't know the percentage. It took a few weeks of playing to finish it, partly becuase I was new to Civ and pretty slow... plus it taught me a lot along the way. It was so boring that I have never tried to get a score that high again.
I remember that along about 1950, after I had pre-planned exactly where all my remaining cities should be constructed, I discovered the 254 (plus one for the Sioux) city limit when I tried to build.. Boy, was I hacked... I could not believe there was such a low limit on # of cities!! I actually had to destroy several cities (building engineers) and go with the 254 best, which put me right up on the 2020 deadline for them to grow. Boy it was frustrating and tedious!
BTW, that was the game in which I discovered the value of trade... before then, I never bothered with trade routes.