Interesting profile - my thoughts with the caveat that I’m just another amateur trying to learn for myself what works and what doesn’t!
You weren’t overreaching as much as I expected You have really solid 1-1.5 hr power and compliance on a lot of tough 90 min indoor workouts even with your rising FTP. You had an 80 min outdoor ride earlier this month with NP ending around your FTP - that’s strong and no surprise you raised FTP again after all of that! And the 50 mile you rode 9/4 - wow - so much power variation regularly going to 2X+ over FTP - but you obviously survived. Point being, with the limited outdoor rides you have, you seem to have demonstrated up to 50 miles, you can ride with some pretty intense variability way over your FTP.
Given all that, I can see why you’re perplexed that you cramped up 40 miles in - if the ride ended at 40 miles, I wouldn’t say it looked like you were overreaching compared to what you’ve demonstrated previously for similar duration.
Something else that I saw was a couple breaks early, one rather long. Also keep in mind the actual NP/average power you did was a good bit lower than what TR says since TR doesn’t average down over those breaks. That only makes it more surprising that you had cramps as that should give you a lot of recovery time - it makes me wonder if those early breaks were doing more harm than good, especially when you went back out and smashed hard right up the climb after the second longer one? Maybe something to consider as it was also very different from your normal riding pattern?
All that being said, while you’ve shown you’re good to ride hard for 40-50 miles, I would not survive a century very well with the way you rode those first 40 miles - particularly the number of times you were hitting 1.5-2x your FTP. I’m learning that burning matches like that is a surefire recipe for cramps if I’m doing a 70+ mile ride. For weekly 2 hr club rides, that kind of variability doesn’t hurt me, but I find I get a much better result in the long rides if I pace things with a much tighter power ceiling. That can mean losing a group in a fondo/endurance race, but you’d be surprised how many times you’ll later pass some of that same group as they’ve cramped up down the road.
As a contrast, I’ll share a similar climbing century ride that for me worked out well recently - you can see a pretty tight ceiling on power - until 4 hrs / 70 miles in, where I intentionally put in a pretty hard climb effort because I felt good - and that nearly did me in - had to fight some cramps off after that and barely recovered.
I can find other examples of long rides in my history where I didn’t pace as well, too many short surges, and I paid the price. (and then made excuses about hydration…)
You might find it interesting to see how far you can go maintaining very strict discipline with a ceiling on power - say target ~190W (70%) evenly across most terrain - and let yourself go up to a maximum of ~250W only when on a true climb - keep this SS time down to only 20% of your ride. And then see how you feel hour by hour. Aside from being good pacing practice, I’d bet that just by spending that strong 1-2 hr fitness more judiciously over time, you’ll immediately set power PRs all across the 2-5 hr range. It’ll feel silly at times when you don’t just jump up and hammer across every short rise - but it helps you keep going for a long time at a solid pace. And if you still crash and burn too fast, then you really know you need to just spend a lot more time riding long Z2!
My goal for next year is to not be quite so restricted in making efforts above FTP on long rides - consensus on here seems to be that lots and lots of SS time in long intervals to build endurance is the way to go more than VO2 max type work. We’ll see…