Well my FTP sucks but I know I can hold it for an hour. I used TR 8 min, outside 20 min, TR ramp and Xert along with Golden Cheetah and the good old Max Power Curve with some modeling. Guess what? For me, they all fall within 5%. With Xert and Golden Cheetah as long as you do some max efforts at a couple of durations its gonna get ya really close. If you can pace 8 min, 20 min or the TR ramp, you should get a decent result. Caveat here is people that dont have the fatigue resistance might get a higher FTP number but cant hold it for the hour. I know some people who can get a high 20 min but Ive never seen them get close to holding it for an hour. If you are struggling with workouts, adjust that intensity!