Simply go as hard as you can. You don’t want to do a field test ‘by the numbers’ - you gotta learn what it feels like to go as hard as you can bc you’ll need to be able to do that in your races or events.
What if you’ve improved by 20%? I am a glass half full kinda coach and if you started off at an arbitrarily selected 8-10% you’d be leaving some watts on the table. That is why as hard as you can by feel is THE BEST
Pro tip - pace properly & do not go out too hard - 265 watts for the 1st two minutes and then after that as hard as you can by feel.
Have you read our training tip on field testing?
Phil Gaimon and I talk about warm up and eating pre-test here (do not eat a gel during the test