Regarding use of the Coros Personalized Marathon Plan.
I ran Boston this year. I'm 215lbs, and about to turn 55. I run often, but I hesitate to call myself a runner. Obstacle Races are the only events I do well at. In 2024 I ran Boston, it was very hot and I crashed for a number of reasons, but primarily an inability to take in as much fluid as I was losing. My training plan for that one was haphazard. I ran over 20 miles 4 times, but didn't really track my pace except on Marathon pace runs and the treadmill. I finished in 4:16.
This time I used a Coros plan. My running fitness had me at a predicted 3:41 finish just before I started. I did crash my fitness a bit by running in deep snow for a week. (The watch detected a significantly higher than normal heart rate for the pace I was keeping). Thus, I ended up starting the plan with a predicted finish time of 3:57. That irritated me.
I stuck to the plan almost exactly, despite getting a two week long cold, and having an unusually cold winter here in Boston. 90% of my runs were outside, and I only moved two of them by one day. My fitness improved slower than I thought it would and at the end of the 15 weeks, it was predicting 3:49 finish. Longest run was 17.8. 4 of the last 6 weeks were quite challenging with the intervals and fartleks.
I had a good nutrition plan, Maurten plus a couple salt stick gummy packs that I planned on taking a few miles before the hills, and Gatorade on the course. I kept an very consistent pace of around 8:49-8:55. I slowed down a bit on the hills but ran them comfortably. Last few miles hurt. Finished in 3:55.
The plan definitely worked. I was hoping to finish a bit faster, but Boston is tough. I think the plan could have pushed me a bit more, but I also didn't get the most aggressive plan as my prior month mileage was below normal. I'm pretty satisfied with the results, all in all. I do wish there was an option to increase the difficulty slightly mid program, though this could also cause people to crash out.
Anyway, I recommend giving it a shot. I would if I did another.