I would say that will depend on the rider and the level of pain they want to go through. Some ballpark figures: A pro-level male athlete can comfortable put out

I would say that will depend on the rider and the level of pain they want to go through. Some ballpark figures: A pro-level male athlete can comfortable put out 200W without breaking a sweat. All-out effort for an elite rider (male) is upwards of 400W for 20+ min effort. (According to Strava records Van der Poel has put out 450W for 20min) A pro-level female rider can put out 300-350W continuously for an hour (and longer) in all-out effort. A semi-untrained (male) individual can put out ~150-200W on average for an hour of all-out effort. 180W is ~30km/h for an amateur rider in a comfort position on a endurance geometry racing bike with system weight of 80kg. A semi-untrained rider would consider 90-130W acceptable for a leisure ride. These figures are quite less useless, you've to put them in perspective with the system weight (bike + rider), just can't escape physics.