In all of my attempts, it's been 15 minutes of trying to be consistent, and 5 minutes of trying to keep the pedals turning without throwing up. I am terrible at regulating at/near threshold. Now Z2? I can peg 135bpm / 170W and just stay there all day.

My last FTP test I got to the 20-minute mark, cooled down, then rode another 20 miles in a loop to get home. So clearly, I had not given it that 100%. I'm not sure I ever have.