Also, 30 kph is practically the top speed for a majority of cyclists - there's a level, narrow, short (200 m), 30-max-speed, all-traffic (except pedestrians) tunnel on my usual route. Do I temporarily reach 30 kph there, in order to be polite and get out of there as fast as possible? Yes, with some difficulty. (Do drivers honk at me for being unbearably slow while going the max legal speed? Yes.)

So, I'd say a typical city scenario is <20 kph, more than halving the estimate.