30km/h is doable with some minor effort, sure, but it's not exactly common. You'll be held up by other bikes constantly on most roads this applies to.

50km/h is for athletes or going down steep hills. If you're training for the tour de france in some random neighbourhood in Amsterdam, I think you're doing something wrong.

50 is literally faster than Tour de France pros maintain on flat ground. A regular person on a normal bike will have a hard time even doing 30.

Thanks for pointing that out.. Maybe 35km/h is a more reasonable ceiling.

The reason I mentioned this number is because I found this article of some Norwegian middle aged woman saying she is reaching 50km/h explaining something with the speed limit of bicycles in Norway.

However she meant that she reaches that speed downhill, which makes sense..

https://elbil.no/lovlig-elsykkel-i-508-km-t/

50 sustained is trained athlete level. Normal cyclists can't do that for any length of time.