Your theoretical top speed will be 42.36 km/h
http://www.bikecalc.com/speed_at_cadence
At over 25 km/h you are going to need to fight air resistance and that is where the motor comes in... I am a reasonably fit 60+ yr old man weighing about 80 kg on a bike weighing 23+ kg. I have ergotec flat pedals and a moon bar so I am sitting up reasonably straight.
If I de-restrict and use assistance level 5 I have my Watts, about 150 - 160 + motor Watts of up to 500 depending on the state of the battery say 650W. If you punch those numbers into any online bike calculator you will see that 45 km/h is possible on a 250 W pedelec if you have the right gearing.
Watch out for cars! They see a bike and guess you are doing 20 km/h and not the double...