There's an old thread on here I'm having trouble finding at the moment - I'll edit this with a link if I can find it. Mike Page stated that at least a 650 would probably be needed to hit 100. I think it's more nuanced than that to be honest.
I don't know what my Fargo is, and probably won't ever. I just don't get out enough to play in 9 Ball tournaments, let alone those that report to Fargo. My guess is I'm around 650-675. This is an absolute guess. My high run is 101. Been in the 70s many times, 80s and 90s a few times. I do not play a lot of rotation games anymore.
The reason I say it's nuanced is straight pool has a much, much steeper learning curve than I had really anticipated. About a year ago, after getting a home table, I set a goal of running 100. Prior to that, I really only played 9 or 10 ball the few times a month I'd go to the pool hall. In about a 9 month span, I got up to 74. Bunch of 40s, 50s, and 60s, and one 74. Then I took a break (summer time means I focus on other things - golf, running, cycling, etc.).
In that time frame, it became immediately apparently that 14.1 and 9/10 ball are two completely different games. The emphasis on execution and angle management in 9/10 ball just isn't enough to produce high runs in 14.1 consistently. The speed control in 9/10 ball is helpful, but speed control is much more refined in 14.1. I found that there's a lot of conventional wisdom about 14.1 that is true like 51% of the time. The classic side pocket key ball? If there isn't a solid pattern to get near perfect on that key ball, I'll look for something that's better. You get bad on that ball, there's a good chance the run is over, and the margin of error on that ball can be pretty small. I learned that you need to get comfortable shooting off angle into side pockets and shooting balls up table to open up patterns. The idea that you are shooting easy shots a lot more is true in a small sense - you've got to make difficult shots in 14.1 too, but the margin of error in position on both easy and difficult shots is way smaller - cinching balls will end a run eventually in 14.1. IMO, Recovering in 14.1 is more difficult than in 9/10 ball, which seems counter intuitive because you have more options in 14.1. Running into a ball accidentally will more often than not tie something up, or block something, and it will kill a run. Intentionally opening a cluster up is also tough - you need an insurance ball, plus you need to not tie something else up or block another ball after the cluster. You need to learn to manufacture break balls, but learn to manufacture key balls too. Learn when to give up a tough pattern for a side of the rack breakshot for an easier pattern to an under the rack breakshot. The list goes on and on.
Then there's patterns, which is its own topic. My patterns have gotten much better, but there's still room for a lot, and I mean a lot, of improvement. And then there's breakshots, which is also its own topic.
So I guess, why do your runs end? Are you making balls consistently but scrambling at the end and not getting on the break ball, or missing a tough shot at the end of the rack? Are you getting stuck mid-rack? Are you missing break shots?
I write all this because I'm not sure Fargo really captures all of the many puzzles pieces that goes into 14.1 play. Sure, a guy that's 700+ probably has the tool set to hit 100 or more eventually. But there's a lot to 14.1 that a ~600 level player can probably work on to get them north of 60 by really working on the game.
And then there's luck. You don't always get a shot after the break, even if the balls are all open with no clusters. Sometimes the balls open funny. Sometimes you get kicked way up table, or into a pocket after the break. Sometimes you do get lucky and bump a ball into a break shot, or into a key ball.
My worthless $0.02: straight pool is like another language. Total immersion is probably the best way to learn to speak it. You can probably make some gains that your Fargo Rate might not indicate are possible.