Under/overs for 3x9min. I went to go check back to last year's data. Same training bike from the gym at work, 70 watts higher for the same workout on almost the same date from 2017 to 2018.
I don't think anywhere close to that is possible for 2018 to 2019, but maybe a 1/3 would be stellar even.
https://www.strava.com/activities/1792323400